CN114018898B - Forsterite crystal orientation method based on polarized laser Raman spectrum - Google Patents

Forsterite crystal orientation method based on polarized laser Raman spectrum Download PDF

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CN114018898B
CN114018898B CN202111311280.4A CN202111311280A CN114018898B CN 114018898 B CN114018898 B CN 114018898B CN 202111311280 A CN202111311280 A CN 202111311280A CN 114018898 B CN114018898 B CN 114018898B
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李晓光
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Abstract

The invention relates to a forsterite crystal orientation method based on polarized laser Raman spectrum, which comprises the steps of preparing a sample to be detected, obtaining Raman spectrum information, calculating a Raman peak integral area ratio, carrying out polar coordinate projection according to a correlation coefficient, determining an included angle between a detected crystal face and a z crystal axis and an included angle between the detected crystal face and an x or y crystal axis in a polar coordinate system, and judging the crystal face. The invention establishes a polarization Raman spectrogram model of the forsterite crystal for the first time, and obtains a crystal axis orientation method of the forsterite crystal grains to orient the forsterite crystal in the mineral rock slice according to the measurement result of the polarization Raman spectrum. The crystal orientation method is efficient and accurate, and the forsterite is oriented to three crystal axes in a three-dimensional space for the first time.

Description

Forsterite crystal orientation method based on polarized laser Raman spectrum
Technical Field
The invention belongs to the field of mineral crystal sample detection, and particularly relates to a forsterite crystal orientation method based on polarized laser Raman spectroscopy. The method can conveniently and simply obtain the crystal axis orientation of the forsterite crystal grains in the mineral sheet or the hand specimen.
Background
In the field research, mineral rocks are often ground into plane sheets to be tested in various scientific tests, mineral crystals have anisotropic characteristics, and many properties of minerals are influenced by the anisotropic characteristics. Therefore, researchers invented various crystal orientation methods.
By crystal orientation, it is meant that the entire grain will be located in a coordinate system centered on the crystal particle. The olivine belongs to the orthorhombic system, and the chemical formula can be expressed as (Mg, Fe)2[SiO4]The chemical formula does not contain hydroxyl and belongs to a nominal anhydrous mineral, but in recent years, the research finds that the crystal lattice has the hydroxyl with the content of ppm (one millionth), the crystal lattice is commonly called as water in the earth science research, and the water significantly influences the mineralPhysical and chemical properties. Due to its extremely low water content, it is difficult to accurately quantify it using conventional testing methods, and current testing techniques mainly include infrared spectroscopy, but their crystal axis effects are very significant, possibly resulting in over ten times of testing errors. Therefore, the crystal orientation of the ground sample is required. Conventional crystal orientation methods include polarization microscopy, which is relatively crude in orientation and difficult to provide digitized scientific data. The optical goniometer orientation method is based on large size crystals; the X-ray diffraction method can also obtain the orientation information of the crystal, and the single crystal diffraction requires 360-degree rotation of the crystal to obtain a diffraction signal, so the process is complicated; the electron back scattering diffraction technology is an ideal method for orienting the flake mineral at present, but the electron back scattering has extremely high requirements on the preparation and the test of the surface of a sample, and only tens of nanometers of atom arrangement information below the surface can be analyzed, the flatness of a grinding and polishing sample and the residual stress structure of the surface of the mineral have great influence on the identification of the chrysanthemum pool pattern, and the crystal orientation of the whole particle is difficult to accurately position in a depth range. For example, CN112394073A discloses a method for rapidly and accurately determining the crystal axis orientation of gallium oxide single crystal, but its initial analysis condition is based on the unidirectional growth characteristics of crystal fiber, i.e. the initial (010) crystal face needs to be determined by naked eyes. The off-angle of the crystal plane was then measured by an X-ray orientation. CN111267249A discloses a method for acquiring diffraction data of the measured crystal by using a single crystal diffractometer. At present, the polarization raman spectroscopy has obtained an application example in the crystal axis orientation measurement of a part of two-dimensional nano materials with simpler molecular structures, but most of the two-dimensional nano materials are based on a measurement method that the two-dimensional materials are vertical to a (001) crystal face, the molecular arrangement types of the two-dimensional materials in an XY plane are few, and relevant direction parameters can be extracted. However, the research and application of the orientation method aiming at the three-dimensional mineral are few, and a crystal axis measuring method aiming at the nominal anhydrous mineral is not available.
As described above, the measurement of the crystal axis orientation requires a high level of crystal, requires a high level of sample processing technique, and is highly dependent on the equipment, and therefore the range of application is limited, and these methods do not provide the most desirable effects for this type of sample.
Disclosure of Invention
In order to solve the problem that the existing laboratory tests the crystal axis orientation of the forsterite crystal grains fussy, the invention establishes a polarization Raman spectrogram model of the forsterite crystal, determines the crystal axis orientation of the forsterite crystal grains according to the measurement result of the polarization Raman spectrum, and discloses a crystal orientation method for forsterite in a mineral rock slice. The invention firstly orients the three crystal axes of the forsterite in a three-dimensional space.
When a medium is irradiated by monochromatic light, phenomena such as scattering, reflection, absorption, transmission and the like are generated. The scattered light can be classified into two types according to the energy difference, wherein the component with the same frequency as the incident light frequency is called Rayleigh scattering; the frequencies of the spectral lines are symmetrically distributed on two sides, wherein the lower frequency is called a Stokes line, and the higher frequency is called an anti-Stokes line, namely the Raman spectrum.
Based on the characteristics of polarized laser, the vibration direction of the crystal is vertical to the propagation direction, the crystal can be completely absorbed in the vibration direction, and the molecular structure in the vertical direction cannot absorb the polarized laser, so that the symmetry of the crystal can be reflected by a signal of a polarized Raman spectrum. Based on group theory analysis and Raman tensor, the method for determining the crystal direction of forsterite is provided based on the principle that different absorption rates can be generated on the anisotropic crystal structure under the same laser after the depolarization degree of the mineral crystal structure is determined by determining the polarization selection effect of the mineral crystal structure, and the scattered Raman spectrum is in a certain proportion.
The crystal structure of forsterite is shown as monoisland silicate, O is approximately closest packed parallel to (100), silicon fills the tetrahedral pores of 1/8 therein to form silicon-oxygen tetrahedrons, and magnesium or iron ions fill the tetrahedral pores of 1/2 therein to form [ MO ]6]The octahedrons, adjacent octahedrons share the vertex, form the octahedral chain similar to saw-toothed shape. Alternating layers shared [ SiO ]6]The vertices and edges of tetrahedrons. Such a crystal structure exhibits anisotropic selectivity when absorbing raman spectra. The strongest Raman vibration peak of forsterite is 855.0cm-1、824.0cm-1Belonging to the vibration mode of Si-O, M-O, and therefore, can be selectively absorbedThe principle of specific excitation laser reflects the spatial orientation of the main crystal structure.
TABLE 1 Raman vibration mode assignment of forsterite
Vibration mode Raman shift Vibration attribution
Ag 965.0(m) V3
B3g 919.0(w) V3
B2g 882.0(w) V3
Ag 856.0(vs) V1+V3
Ag 824.0(s) V1+V3
Ag 608.0(w) V4
B1g+B2g+B3g 589.0(w) V4
Ag 544.0(w) V4
B1g+B2g+B3g 433.5(w) V2
B3g 374.0(w) mix(M2 trans)
Ag 337.0(w) M2 translation
Ag 329.0(w) SiO4 rotation
B3g 314.0(vw) mix(SiO rot)
Ag 303.0(w) M2 translation
Ag 225.0(w) SiO4 translation
The invention relates to a forsterite crystal orientation method based on polarized laser Raman spectrum, which comprises the following steps:
(1) preparing a sample to be tested: preparing a forsterite sample to be detected into a flaky mineral or a mineral with a surface morphology containing a plane to be detected, so that the directional reference is facilitated; further, the sample to be detected in the step (1) is in the shape of particles or flakes capable of performing orientation in a three-dimensional space
(2) Obtaining Raman spectrum information: testing the raman spectrum of forsterite in the mineral flakes; and rotated through different angles to acquire a series of angularly related raman spectra.
The method comprises the steps of positioning forsterite in a mineral sheet, rotating the forsterite for 360 degrees in a circle, testing the Raman spectrum of the forsterite by using polarized laser excitation, collecting the Raman spectrum at intervals of 0-10 degrees, and acquiring a series of Raman spectra related to angles in the period. The obtained series of raman spectra were classified into four types, and the spectrum in the range of 360 ° is generally classified into four types.
In the range of rotating 360 degrees, the Raman peak intensity of a certain crystal face has four periods, namely every 90 degrees is a change period of the crystal face, spectrograms in the range of 90 degrees (if the peak is tested at every 10 degrees, the total number of the spectrograms is 9) are selected to count the value range of the crystal face according to the change rule from the strongest to the weakest of the certain peak, the value range is not consistent with the crystal face at the test surface of other crystal faces, and therefore, the Raman spectrum information related to a series of angles is extracted to serve as one of the judgment conditions.
(3) Calculating the integral area ratio of the Raman peak: calibrating the peak position of the Raman peak in the measured Raman spectrum, and observing the change condition of each Raman peak in the Raman spectrum along with the rotation angle for subsequent analysis; and fitting and peak splitting are carried out on the characteristic Raman peak to obtain an integral area, and the ratio of the Raman peak in the measured Raman spectrum is made according to the integral area of the Raman peak for subsequent analysis.
The invention selects the ratio of the integral areas of the Raman spectrogram instead of simply extracting the peak intensity, is more accurate than independently extracting the peak intensity, is easier to distinguish the change rule, and eliminates the peak intensity change caused by the difference of signal-to-noise ratios among different batches of measurements.
According to the characteristics of the self-Raman vibration mode of the forsterite, the method firstly performs baseline deduction on a V1+ V3 vibration Raman peak, calculates the integral area ratio, and then calculates the integral area ratio of the Ag vibration peak.
The specific process is as follows: for forsterite 856cm-1And 824cm-1The V1+ V3 vibration Raman peak of the image is subjected to baseline subtraction, and the integrated area of the image is subjected to ratio
Figure BDA0003341933330000041
And a series AgIntegral area ratio of vibration peak
Figure BDA0003341933330000042
Figure BDA0003341933330000043
(4) Performing polar coordinate projection according to the value of the correlation coefficient R:
firstly, determining a polar coordinate projection diagram of a standard crystal face: forsterite (110), (120), (010),
Figure BDA0003341933330000044
(001) And taking the typical crystal face as a standard crystal face, extracting data parameter characteristics, performing polar coordinate projection of an R value to obtain a polar coordinate projection of the standard crystal face, and taking the polar coordinate projection as a basis for positioning crystals of other arbitrary crystal faces.
If the Raman spectrogram is not consistent with the standard crystal plane, the projection distances Rmax and Rmin in the two directions of the long axis and the short axis are calculated to be M/2 and N/2, and the relation between the measured crystal plane and the x, y and z crystal axes and the crystal orientation are determined.
Specifically, a polar coordinate system is set with the rotation angle as an independent variable and the coefficient R as a dependent variable, and then curve fitting is performed on the point projection results, and projection distances Rmax and Rmin in both the major and minor axes directions are calculated for the formed curves as M/2 and N/2.
(5) Determining the included angle between the measured crystal face and the z crystal axis in a polar coordinate system:
and continuously arranging the spectrograms according to angles, and carrying out crystal orientation according to the calculated R value range of the Raman peak. And judging the relation between the measured crystal plane and the z-axis according to the projection distance of the major axis M and the minor axis N.
The specific process is as follows:
a. the 882cm of vibration from V3 is not generated on the same side when the laser propagates along the Z crystal axis of forsterite-1、919cm-1A Raman peak, therefore, when the Raman spectrogram does not have the Raman peak and the Raman peak does not have the Raman peak, the value range of R is 0.5-1.3; 824cm belonging to Ag vibration mode-1And 965cm-1Raman peak, ratio of peak-integrated areas thereof
Figure BDA0003341933330000051
If the value range is 4.5-7, judging that the incident direction (the measured crystal face) is vertical to the z-axis direction of the forsterite crystal;
b. in contrast, when there is a significant 882cm-1And/or 919cm-1Raman peak, the incident direction is not perpendicular to the z-axis direction of the forsterite crystal. Performing polar coordinate projection on the numerical value and the angle value of R, wherein Rmax is recorded as an M/2 value, Rmin is recorded as an N/2 value, the extension direction of the intercept of the direction indicated by the value M of Rmax on a coordinate axis (such as the direction of an arrow M in FIG. 17) is the vertical projection direction of the z-crystal axis on the sample sheet, and the included angle alpha between the measured crystal plane and the z-crystal axis satisfies the following formula;
Figure BDA0003341933330000052
wherein Rmax is in the course of rotation
Figure BDA0003341933330000053
The position of Rmax corresponds to the M direction.
(6) Determining the included angle between the measured crystal face and the x or y crystal axis, and the crystal face:
A. if R isminThe value is less than or equal to 0.40, the included angle between the measured crystal plane and the x-crystal axis is 90 degrees and is (100),
Figure BDA0003341933330000061
A typical crystal plane;
B. if 0.40 < RminIf the angle theta between the measured crystal face and the x-crystal axis is less than 1.00, the included angle theta between the measured crystal face and the x-crystal axis satisfies the following formula:
Rmin=2.62-2.22sinθ
the included angle theta between the interval and the x-crystal axis is about 90 degrees to 47 degrees (theta is more than or equal to 47 and less than 90 degrees);
C. if 1.00 < RminIf the angle theta between the measured crystal face and the x crystal axis is less than 1.25, the following formula is satisfied:
Rmin=1.25-0.35sinθ
the included angle theta between the interval and the X crystal axis is about 47 degrees (not included) to 0 degrees (0 is more than or equal to theta and less than 47);
D. if R isminIf the value is more than or equal to 1.25, the measured crystal face is parallel to the x crystal axis;
further, if
Figure BDA0003341933330000062
The value range is 5-20, and the content of the active ingredient,
Figure BDA0003341933330000063
the value range is 2-8, and the content of the active carbon is,
Figure BDA0003341933330000064
the value range is 1-5, the crystal face (010) or (010) can be judged to be close to
Figure BDA0003341933330000065
Wherein Rmin is in the rotating process
Figure BDA0003341933330000066
And the position of Rmin corresponds to the N direction.
In the invention, because the R value is continuously changed in the test process, the directions of the maximum value and the minimum value, namely the M or N directions, are found through polar coordinate projection.
And according to the determined included angle between the measured crystal face and the x crystal axis, obtaining that the included angle between the measured crystal face and the y crystal axis is 90-theta.
The fitting peak-splitting method comprises one or more of Lorentz fitting, Gaussian fitting and Lorentz-Gaussian mixture fitting.
According to the self-Raman vibration mode of the forsterite, information such as Raman spectrum peaks, integral areas and ratios are firstly obtained, different correlation coefficient R values are calculated, the projection distances of the long axis M and the short axis N are used for judging the angular relationship (a and b) between the test plane and the crystal axis Z, and then the angular relationship between the test plane and the crystal axis X, Y is further determined according to four condition ranges (A, B, C, D) of the correlation coefficient R values, so that the crystal orientation of the forsterite is obtained.
The present invention also provides a computer-readable storage medium storing a computer program which, when executed by a processor, performs the steps of any of the above-described methods for determining the crystal orientation of forsterite.
According to the method for determining the crystal orientation of the forsterite crystal by utilizing the polarized laser Raman spectrum information, the acquisition efficiency of the Raman spectrum information is improved, a polarized Raman spectrogram model of the forsterite crystal is established, the crystal axis orientation of the forsterite crystal grains is determined according to the determination result of the polarized Raman spectrum, and the crystal orientation of the forsterite in the mineral rock slice is accurately and conveniently determined.
According to the invention, the standard crystal surface Raman spectrum information is collected and simulated, and the sizes and the directions of M and N in the three-dimensional polar coordinate are determined according to the numerical value ranges and the position angle relations of a series of related parameters such as R value, Rmax, Rmin and the like, so that the testing method is simple, accurate and efficient.
Drawings
FIG. 1 shows forsterite (110), (120), (010),
Figure BDA0003341933330000071
Polar projection of crystal plane M/N values;
FIG. 2 is a representative Raman spectrum of forsterite of example 1;
FIG. 3 is a graph showing the relationship between the R value and the test rotation angle in example 1;
FIG. 4 is a representative Raman spectrum of forsterite of example 2;
FIG. 5 is a graph showing the relationship between the R value and the test rotation angle in example 2;
FIG. 6 is a forsterite (010) crystal plane Raman spectrum;
FIG. 7 is a representative Raman spectrum of forsterite of example 3;
FIG. 8 is a graph showing the relationship between the R value and the test rotation angle in example 3;
FIG. 9 is a representative Raman spectrum of forsterite of example 4;
FIG. 10 is a graph showing the relationship between the R value and the test rotation angle in example 4;
FIG. 11 is a representative Raman spectrum of forsterite from example 5;
FIG. 12 is a graph showing the relationship between the R value and the test rotation angle in example 5;
FIG. 13 is a representative Raman spectrum of forsterite of example 6;
FIG. 14 is a graph showing the relationship between the R value and the test rotation angle in example 6;
FIG. 15 is a representative Raman spectrum of forsterite from example 7;
FIG. 16 is a graph showing the relationship between the R value and the test rotation angle in example 7;
FIG. 17 shows M, N directions in the polar coordinates of M/N value of the crystal plane of forsterite (110).
In FIG. 1, 1 is a polar projection view of the M/N value of the (110) crystal plane, 2 is a polar projection view of the M/N value of the (120) crystal plane, 3 is a polar projection view of the M/N value of the (010) crystal plane, and 4 is
Figure BDA0003341933330000081
Projection of the M/N values of the crystal plane on a polar coordinate system, 5 is
Figure BDA0003341933330000082
Projection of the M/N values of the crystal plane on polar coordinates.
Detailed Description
Firstly, extracting data parameter characteristics according to a typical crystal face, projecting a polar coordinate projection diagram of an N/N value to obtain the polar coordinate projection diagram of the typical crystal face, and taking the polar coordinate projection diagram as the basis of crystal positioning of other arbitrary crystal faces.
The crystal orientation method of the invention is adopted to respectively orient the forsterite (110), (120), (010),
Figure BDA0003341933330000083
Figure BDA0003341933330000084
The polar projection of the M/N values of the typical crystal planes is performed, and the results of the Raman spectrum and the polar projection of each typical crystal plane are shown in FIG. 1. The obtained polar coordinate projection of the typical crystal face is studied to make three-dimensional crystal orientation for any other crystal face.
Example 1
(1) Preparing a sample to be tested: selecting a sample to be tested of a crystal grown up from forsterite by about 1.5 cm, determining the z-crystal axis direction of the sample by visual observation, and grinding the top surface of the sample to be tested to be a plane along the direction vertical to the z-crystal axis; therefore, the test plane was found to be the (001) plane.
(2) Obtaining Raman spectrum information: vertically testing the Raman spectrum by using the polarized Raman spectrum, and testing the Raman spectrum at intervals of 10 degrees to obtain 36 spectrum data; due to the distribution characteristics of crystal anisotropy, the data can be divided into four sets of spectra with similar characteristics, one of which is shown in FIG. 2, and calculated and a series of AgThe ratio of the integral area of the vibration peak;
(3) calculating the integral area ratio of the Raman peak: analyzing the data, and calculating 856cm-1And 824cm-1Taking the integral area of Raman peak as ratio
Figure BDA0003341933330000085
See FIG. 3;
(4) performing polar coordinate projection according to the value of the correlation coefficient R: setting a polar coordinate system by taking the rotation angle as an independent variable and the coefficient R as a dependent variable, then performing curve fitting on the point projection result, and calculating projection distances Rmax (M/2) and Rmin (N/2) in the major axis direction and the minor axis direction of the formed curve; the projection distance M/2 of the polar coordinates in two directions of the long axis (0-180 degrees) and the short axis (90-270 degrees) is 1.32, and N/2 is 0.50;
(5) determining the angle in the polar coordinate system: further observation of the Raman spectrum does not appear to be 882cm in the whole rotation test period-1、919cm-1Raman peak, calculated R value is in the range of 0.5-1.3 (see FIG. 3), and
Figure BDA0003341933330000091
according to a, judging that the incident direction is vertical to the z-crystal axis direction of the forsterite crystal; the crystal structure can not excite B2g and B3g vibration in the orientation, so 882cm can not be detected-1、919cm-1And (4) judging the incident direction by combining the Raman peak and the standard crystal face fitting result. Therefore, the crystal orientation judgment conclusion (vertical to the z crystal axis) of the invention is consistent with the incident direction (vertical) of the sample to be detected, and belongs to the (001) crystal face.
Example 2
(1) Preparing a sample to be tested: selecting a forsterite crystal sample with the length of about 1.5 cm, determining the z-crystal axis direction of the forsterite crystal sample through visual observation, and grinding a certain side of the forsterite crystal sample into a plane along the direction parallel to the z-crystal axis;
(2) obtaining Raman spectrum information: vertically testing the Raman spectrum by using the polarized Raman spectrum, and testing the Raman spectrum at intervals of 10 degrees to obtain 36 spectrum data; due to the distribution characteristics of crystal anisotropy, the data can be divided into four groups of spectra with similar characteristics, one of which is shown in fig. 4;
(3) calculating the integral area ratio of the Raman peak: the data was analyzed and processed at 856cm-1And 824cm-1The ratio R is the integral area of the Raman peak, see FIG. 5, and is calculated and a series AgThe ratio of the integral area of the vibration peak;
(4) performing polar coordinate projection according to the value of the correlation coefficient R: setting a polar coordinate system by taking the rotation angle as an independent variable and the coefficient R as a dependent variable, then performing curve fitting on the point projection result, and calculating projection distances Rmax (M/2) and Rmin (N/2) in the two directions of the long axis and the short axis of the formed curve; the projection distance M/2 of the polar coordinates in two directions of the major axis (0-180 degrees) and the minor axis (90-270 degrees) is 4.17 and N/2 is 1.24 through calculation;
(5) determining the included angle between the measured crystal face and the z crystal axis in a polar coordinate system: further observation of the appearance of the Raman spectrum at 882cm over the entire rotation test period-1Raman peak, no 919cm-1Raman Peak, 608cm-1The amplitude of the change along with the angle is larger, and the strength change characteristic is equal to 856cm-1The consistency is kept between the first and the second,
Figure BDA0003341933330000101
the direction of extension of the hyperbola of the M/N value projection is the direction of vertical projection of the z-crystal axis on the sample sheet, and the angle α between the projection and the z-crystal axis is (Rmax-1.3) × 100/3 is 95 °, determined by the condition b.
(6) Determining the included angle between the measured crystal face and the x or y crystal axis, and the crystal face:
and (4) calculating the value of Rmin to be 1.25, and judging that the measured crystal plane is approximately parallel to an x crystal axis, is vertical to a y crystal axis and is close to a (010) crystal plane according to D.
As can be seen from the comparison of the forsterite (010) crystal plane Raman spectra in FIGS. 4 and 6, the crystal orientation judgment conclusion of the invention is consistent with the crystal plane of the sample to be measured, and the crystal orientation method is accurate.
Example 3
(1) Preparing a sample to be tested: selecting a forsterite sample from a common rock slice;
(2) obtaining Raman spectrum information: the polarization raman spectrum was used to vertically test the raman spectrum at intervals of 10 ° and 36 spectra were acquired. A representative raman spectrum thereof is shown in fig. 7;
(3) calculating the integral area ratio of the Raman peak: the data was analyzed and processed at 856cm-1And 824cm-1The ratio R is the integral area of the Raman peak, see FIG. 8, and is calculated and a series AgThe ratio of the integral area of the vibration peak;
(4) performing polar coordinate projection according to the value of the correlation coefficient R: setting a polar coordinate system by taking the rotation angle as an independent variable and the coefficient R as a dependent variable, then performing curve fitting on the point projection result, and calculating projection distances Rmax (M/2) and Rmin (N/2) in the major axis direction and the minor axis direction of the formed curve; calculating the projection distance M/2 of the polar coordinates in two directions of a long axis (0-180 degrees) and a short axis (90-270 degrees) to be 3.43 and N/2 to be 0.76;
(5) determining an included angle between the Z crystal axis and the Z crystal axis in a polar coordinate system: further observation of the appearance of the Raman spectrum at 882cm over the entire rotation test period-1、919cm-1Raman Peak, 965cm-1The amplitude of the change along with the angle is large, and the strength change characteristic is 824cm-1On the contrary, the present invention is not limited to the above-described embodiments,
according to the condition b, the extending direction of the hyperbola of the M/N value projection graph is the vertical projection direction of the z-crystal axis on the sample sheet, and the included angle alpha (Rmax-1.3) 100/3-71 degrees with the z-crystal axis is judged;
(6) determining the included angle between the crystal axis and the x or y crystal axis: and (3) calculating to obtain an Rmin value of 0.76, and judging according to the condition B, wherein the formula of the included angle between the measured crystal face and the x crystal axis is as follows: rmin is 2.62-2.22sin theta;
therefore, the included angle θ between the measured crystal plane and the x-crystal axis is arcsin (2.62-0.76)/2.22 is 56 °.
Example 4
(1) Preparing a sample to be tested: selecting a forsterite sample from a common rock slice;
(2) obtaining Raman spectrum information: the polarization raman spectrum was used to vertically test the raman spectrum at intervals of 10 ° and 36 spectra were acquired. A representative raman spectrum thereof is shown in fig. 9;
(3) calculating the ratio of the integral area of the Raman peak: the data was analyzed and processed at 856cm-1And 824cm-1The ratio R is the integral area of the Raman peak, see FIG. 10, and is calculated and a series AgThe ratio of the integral area of the vibration peak;
(4) performing polar coordinate projection according to the value of the correlation coefficient R: setting a polar coordinate system by taking the rotation angle as an independent variable and the coefficient R as a dependent variable, and calculating that the projection distance M/2 of the polar coordinate in two directions of a long axis (0-180 degrees) and a short axis (90-270 degrees) is 2.13 and the N/2 is 0.54;
(5) determining an included angle between the Z crystal axis and the Z crystal axis in a polar coordinate system: further review of FIG. 7The Raman spectrum appears 882cm in the whole rotation test period-1、919cm-1Raman Peak, 608cm-1、882cm-1、965cm-1The amplitude of the change along with the angle is small;
according to the condition b, the extending direction of the hyperbola of the M/N value projection is the vertical projection direction of the z-crystal axis on the sample sheet (about 60 ° to 240 ° direction in fig. 10), and the included angle α between this direction and the z-crystal axis is (Rmax-1.3) × 100/3 is 28 °;
(6) determining the included angle between the crystal axis and the x or y crystal axis:
and (4) calculating to obtain an Rmin value of 0.54, and judging that the included angle between the measured crystal plane and the x-crystal axis is Rmin 2.62-2.22sin theta according to the condition B, so that the included angle theta between the measured crystal plane and the x-crystal axis is arcsin (2.62-0.54)/2.22 is 69 degrees.
Example 5
(1) Preparing a sample to be tested: selecting a forsterite sample from a common rock slice;
(2) obtaining Raman spectrum information: the polarization raman spectrum was used to vertically test the raman spectrum at intervals of 10 ° and 36 spectra were acquired. A representative raman spectrum thereof is shown in fig. 11;
(3) calculating the integral area ratio of the Raman peak: the data was analyzed and processed at 856cm-1And 824cm-1The ratio R is taken as the integral area of the Raman peak, which is shown in figure 12;
(4) performing polar coordinate projection according to the value of the correlation coefficient R: setting a polar coordinate system by taking the rotation angle as an independent variable and the coefficient R as a dependent variable, and calculating that the projection distance M/2 in two directions of a long axis (0-180 degrees) and a short axis (90-270 degrees) is 4.11 and N/2 is 0.45;
(5) determining an included angle between the Z crystal axis and the Z crystal axis in a polar coordinate system: further observation of FIG. 11 shows that the Raman spectrum does not appear at 608cm throughout the entire rotation test period-1、882cm-1Raman Peak 919cm-1、965cm-1The amplitude of the change along with the angle is small;
according to the condition b, the extending direction of the hyperbola of the M/N value projection is the vertical projection direction of the z-crystal axis on the sample sheet (about 60 ° to 240 ° direction in fig. 12), and the included angle α between this direction and the z-crystal axis is (Rmax-1.3) × 100/3 is 93 °;
(6) determining the included angle between the crystal axis and the x or y crystal axis:
and (4) calculating to obtain an Rmin value of 0.45, and judging that the included angle between the measured crystal plane and the x-crystal axis is 2.62-2.22sin theta according to the condition B, so that the included angle theta between the measured crystal plane and the x-crystal axis is arcsin (2.62-0.45)/2.22 is 78 degrees.
Example 6
(1) Preparing a sample to be tested: selecting a forsterite sample from a common rock slice;
(2) obtaining Raman spectrum information: the polarization raman spectrum was used to test it vertically, with 18 spectra being acquired at 10 ° intervals. A representative raman spectrum thereof is shown in fig. 13;
(3) calculating the integral area ratio of the Raman peak: the data was analyzed and processed at 856cm-1And 824cm-1The ratio R is the integrated area of the raman peak, see fig. 14;
(4) performing polar coordinate projection according to the value of the correlation coefficient R: setting a polar coordinate system by taking the rotation angle as an independent variable and the coefficient R as a dependent variable, and calculating the projection distance M/2 of the polar coordinate system in two directions of a long axis (0-180 degrees) and a short axis (90-270 degrees) to be 3.84 and N/2 to be 0.39;
(5) determining an included angle between the Z crystal axis and the Z crystal axis in a polar coordinate system:
further observation of FIG. 13 shows that the Raman spectrum does not appear at 608cm throughout the entire rotation test period-1、882cm-1Raman Peak, 919cm-1、965cm-1Obviously, the integral area change amplitude is small along with the angle;
according to the condition b, the extending direction of the hyperbola of the M/N value projection is the vertical projection direction of the z-crystal axis on the sample sheet (about 10 ° to 190 ° in fig. 14), and the included angle α between this direction and the z-crystal axis is (Rmax-1.3) × 100/3 is 84 °;
(6) determining the included angle between the crystal axis and the x or y crystal axis:
and calculating to obtain an Rmin value of 0.39, and judging that the included angle between the measured crystal face and the x-crystal axis is 90 degrees according to the condition A.
Example 7
(1) Preparing a sample to be tested: selecting a forsterite sample from a common rock slice;
(2) obtaining Raman spectrum information: the polarization raman spectrum was used to vertically test the raman spectrum at intervals of 10 ° and 36 spectra were acquired. A representative raman spectrum thereof is shown in fig. 15;
(3) calculating the integral area ratio of the Raman peak: the data was analyzed and processed at 856cm-1And 824cm-1The ratio R is taken as the integral area of the raman peak, see fig. 16;
(4) and (3) performing polar coordinate projection according to the value of the correlation coefficient R: setting a polar coordinate system by taking the rotation angle as an independent variable and the coefficient R as a dependent variable, and calculating the projection distance M/2 of the polar coordinate system in two directions of a long axis (0-180 degrees) and a short axis (90-270 degrees) to be 3.90 and N/2 to be 1.16;
(5) determining an included angle between the Z crystal axis and the Z crystal axis in a polar coordinate system: further observation of the Raman spectrum of FIG. 15 is 882cm over the entire rotation test period-1The Raman peak is obvious and the intensity is basically consistent, 919cm-1Raman peak is weaker, 965cm-1The change range along with the angle is obvious and small;
according to the condition b, the extending direction of the hyperbola of the M/N value projection is the vertical projection direction of the z-crystal axis on the sample sheet (about 60 ° to 240 ° direction in fig. 16), and the included angle α between this direction and the z-crystal axis is (Rmax-1.3) × 100/3 is 87 °;
(6) determining the included angle between the crystal axis and the x or y crystal axis:
the value of Rmin is calculated to be 0.45, and according to the condition C, the formula of the included angle between the measured crystal face and the x crystal axis is judged to be Rmin1.25-0.35sin theta, therefore, the angle theta between the measured crystal plane and the x-crystal axis is arcsin (1.25-1.16)/0.35 is 15 deg.
The invention obtains a three-dimensional polar coordinate diagram by utilizing the mechanism that non-polarized light vibrates to the Raman peak of a sample under different rotating angles, thereby obtaining the crystal orientation. If the sample is vertically tested by using the unpolarized light, the Raman peaks obtained in all directions are still consistent after the rotation angle, and the crystal direction information cannot be obtained. Similarly, if polarized light is used in step (2), but the angle test is not rotated, the angle information cannot be obtained, and the characteristic change law of the crystal orientation cannot be recognized.
The invention firstly provides a method for obtaining the three-dimensional polar coordinate of the forsterite crystal according to the Raman peak vibration, so that the technical problems of low judgment precision of naked eyes, high requirement on equipment and the like are effectively solved, and the crystal orientation method is accurate and efficient.
It will be understood by those skilled in the art that the foregoing embodiments are provided merely for clarity of disclosure and are not intended to limit the scope of the invention. Other variations or modifications will be apparent to persons skilled in the art in light of the above disclosure and which are within the scope of the invention.

Claims (5)

1. A forsterite crystal orientation method based on polarized laser Raman spectroscopy is characterized by comprising the following steps:
(1) preparing a sample to be tested: preparing a forsterite sample to be detected into a flaky mineral;
(2) obtaining Raman spectrum information: testing the raman spectrum of forsterite in the mineral flakes; rotating the Raman spectrum by different angles to obtain a series of Raman spectra related to the angles;
(3) calculating the integral area ratio of the Raman peak: calibrating the peak position of the Raman peak in the measured Raman spectrum, and observing the change condition of each Raman peak in the Raman spectrum along with the rotation angle; fitting and peak splitting are carried out on the characteristic Raman peak to obtain an integral area, and a ratio R is made for the Raman peak in the measured Raman spectrum according to the integral area of the Raman peak; the specific process is as follows: for forsterite 856cm-1And 824cm-1Taking the Raman peak as a baseline to deduct, and taking the integral area as a ratio
Figure 852403DEST_PATH_IMAGE001
(ii) a In addition, the vibration peak integral area ratio is further calculated
Figure 596368DEST_PATH_IMAGE002
(ii) a Wherein A is856、A824、A608、A882、A915、A965Are 856cm respectively-1、824cm-1、608cm-1、882cm-1、915cm-1、965cm-1The integrated area of the raman peak of (a);
(4) polar projection is carried out according to the value of the ratio R: setting a polar coordinate system by taking the rotation angle as an independent variable and R as a dependent variable, then performing curve fitting on the point projection result, and calculating projection distances R in the two directions of the long axis and the short axis of the formed curvemax=M/2、Rmin= N/2, where M, N is the major axis length, the minor axis length, respectively, of the formed curve;
(5) determining an included angle between the measured crystal face and a z-crystal axis in a polar coordinate system;
the specific process is as follows:
a. when 882cm does not exist in the Raman spectrum-1、919cm-1Raman peak, and R value range is 0.5-1.3,
Figure 974260DEST_PATH_IMAGE003
the value range is 4.5-7, and the measured crystal face is vertical to the z-axis direction of the forsterite crystal;
b. when the Raman spectrum has obvious 882cm-1And/or 919cm-1Raman peak, the measured crystal face is not vertical to the direction of the z-axis of the forsterite crystal; at the moment, the included angle alpha between the measured crystal plane and the z-crystal axis satisfies the following formula:
Figure 778268DEST_PATH_IMAGE004
(6) determining the included angles of the measured crystal face and an x crystal axis and a y crystal axis, and judging the crystal face;
the determination process of the angle between the measured crystal plane and the x-crystal axis is as follows:
A. if R isminThe included angle between the measured crystal face and the x-crystal axis is 90 degrees when the angle is less than or equal to 0.40;
B. if 0.40 < RminIf the angle between the measured crystal face and the x-crystal axis is less than 1.00, the calculation formula of the included angle theta between the measured crystal face and the x-crystal axis is as follows:
Rmin=2.62-2.22sinθ;
C. if 1.00 < RminIf less than 1.25, the angle between the measured crystal face and the x-crystal axisThe formula for θ is:
Rmin=1.25-0.35sinθ;
D. if R isminIf the value is more than or equal to 1.25, the measured crystal face is parallel to the x crystal axis;
the determination process of the angle between the measured crystal face and the y-crystal axis is as follows: the included angle between the measured crystal face and the y-crystal axis is 90-theta.
2. The method of claim 1, wherein before the step (4), whether the measured crystal plane is a standard crystal plane is determined by using forsterite (110), (120), (010),
Figure 976031DEST_PATH_IMAGE005
Figure 789266DEST_PATH_IMAGE006
(001) as a standard crystal face; if the Raman spectrum of the measured crystal face is not consistent with the standard crystal face, calculating the polar coordinate projection distance R of the measured crystal facemax、RminAnd determining the included angles between the measured crystal face and the x, y and z crystal axes and judging the crystal face.
3. The method of claim 1, wherein R of step (6)minA value of 1.25 or more, and
Figure 756085DEST_PATH_IMAGE007
the value ranges from 5 to 20,
Figure 262153DEST_PATH_IMAGE008
the value range is between 2 and 8,
Figure 681633DEST_PATH_IMAGE009
the value range is 1 to 5, the measured crystal face is judged to be close to the crystal face (010) or
Figure 298559DEST_PATH_IMAGE010
4. The method according to claim 1, wherein the fitting peak separation method in step (3) is Lorentzian fitting, Gaussian fitting or Lorentzian-Gaussian mixture fitting.
5. The method as claimed in claim 1, wherein step (2) is carried out by locating forsterite in the mineral sheet, rotating it by 360 ° and collecting the raman spectrum for every 0-10 ° rotation using polarization raman spectroscopy.
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