CN111855585A

CN111855585A - Method for determining crystal domain space distribution and crystal lattice orientation of non-centrosymmetric crystal

Info

Publication number: CN111855585A
Application number: CN202010644337.1A
Authority: CN
Inventors: 邢晖; 唐国雄; 许祝安
Original assignee: Shanghai Jiaotong University; Zhejiang University ZJU
Current assignee: Shanghai Jiaotong University; Zhejiang University ZJU
Priority date: 2020-07-07
Filing date: 2020-07-07
Publication date: 2020-10-30
Anticipated expiration: 2040-07-07
Also published as: CN111855585B

Abstract

The invention relates to the field of crystal twin structure characterization, in particular to a method for determining the domain space distribution and the lattice orientation of a non-centrosymmetric crystal. The method uses non-centrosymmetric Ca₃Ru₂O₇The crystal is used as a test system, a polarized light reflection principle is utilized, linear polarized light is perpendicularly incident to the surface of the crystal, and contrast distribution of reflected light is formed on the surface of the crystal due to anisotropy of dielectric constant tensor of the non-centrosymmetric crystal, so that domain distribution is imaged. Meanwhile, the difference of the energy band structures of the semi-infinite crystals corresponding to the paired cleavage planes causes the color difference of each non-equivalent cleavage plane, so that the lattice orientation corresponding to the crystal domain can be directly judged through the color of the crystal domain. The method provides imaging of twin crystal space distribution of the non-centrosymmetric crystal, directly determines the crystal lattice orientation, greatly improves the efficiency compared with the traditional crystal domain characterization method, and can be applied to other non-centrosymmetric crystals in an analogy manner.

Description

Method for determining crystal domain space distribution and crystal lattice orientation of non-centrosymmetric crystal

Technical Field

The invention relates to a method for determining the domain space distribution and the lattice orientation of a non-centrosymmetric crystal, belonging to the technical field of crystal twin structure characterization.

Background

In the study of physical properties of crystal materials, the crystal itself is usually required to be a phase-pure structure, and the influence on the intrinsic physical properties of the crystal due to the unevenness of the crystal structure is not desirable. Therefore, before studying the relevant properties of the crystal, the composition and structure of the crystal are characterized and qualified crystals are screened. In the non-centrosymmetric crystal, the ubiquitous existence of crystal domains is a main difficulty in structural characterization of the crystal.

With a representative non-centrosymmetric crystal Ca₃Ru₂O₇For example, because the in-plane lattice constants are very close

The crystals with twins cannot be distinguished by conventional Laue diffraction. In conventional studies, it has been generally confirmed whether or not a twin crystal exists by screening anisotropy of magnetic susceptibility in a crystal plane. However, this method can determine only the direction of the major axis of the domain and does not give the spatial distribution of the twin crystal and the orientation of the crystal lattice within the domain. And the specific operation has more steps, takes long time, is more complex, and the screening efficiency of the crystal is lower. Therefore, there is a need to find a fast and efficient method for determining the spatial distribution of domains and the orientation of crystal lattice in a crystal.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for determining the domain space distribution and the crystal lattice orientation of a non-centrosymmetric crystal, which can quickly and effectively determine the domain space distribution and the crystal lattice orientation of each domain area.

In order to solve the problems, the technical scheme adopted by the invention is as follows:

a method for determining the spatial distribution of crystal domains and the orientation of crystal lattices of non-centrosymmetric crystal includes such steps as imaging by the spatial distribution of crystal domains of polarized light reflecting non-centrosymmetric crystal, cleaving and determining the orientation of crystal lattices.

Further, when the spatial distribution of crystal domains is imaged, the measured non-centrosymmetric crystal is horizontally placed under an epi-microscope, the ab surface of the crystal is kept to be perpendicular to incident light, the positions of a polarizer and an analyzer are fixed, the polarizer and the analyzer are kept to be perpendicular, the position of the crystal is horizontally rotated and adjusted, the color of the surface of the crystal can be seen to correspondingly change along with the change of the position of the crystal, when color stripes are seen on the surface of the crystal, different color regions correspond to different crystal domains, the boundary of the stripes is a domain wall, and the direction parallel to the boundary and the direction vertical to the boundary respectively correspond to the directions of two lattice main shafts.

Further, when cleavage observation is performed, the crystal is cleaved perpendicularly to the c direction to obtain two corresponding non-equivalent cleavage planes CS1 and CS2, the position of the cleaved crystal is adjusted so that the domain wall is parallel to the polarization direction, the same region corresponding to the cleavage planes of CS1 and CS2 is observed, the cleavage planes of CS1 and CS2 and the crystal domains rotated by 90 ° respectively exhibit 4 different colors, and the lattice orientation of the corresponding region can be directly inferred from the 4 colors.

The principle of the invention is that Ca is not centrosymmetric₃Ru₂O₇The crystal is used as a test system, a polarized light reflection principle is utilized, linear polarized light is perpendicularly incident to the surface of the crystal, and contrast distribution of reflected light is formed on the surface of the crystal due to anisotropy of dielectric constant tensor of the non-centrosymmetric crystal, so that domain distribution is imaged. Meanwhile, the difference of the energy band structures of the semi-infinite crystals corresponding to the paired cleavage planes causes the color difference of each non-equivalent cleavage plane, so that the lattice orientation corresponding to the crystal domain can be directly judged through the color of the crystal domain.

Compared with the prior art, the invention has the beneficial effects that:

the determination method is simple and feasible, solves the problem that the conventional method cannot obtain the crystal domain space distribution, avoids complex measurement operation, greatly improves the screening efficiency of the crystal, and can be applied to the screening work of other non-centrosymmetric crystals in an analogy manner.

Drawings

FIG. 1 is a schematic view of the present invention for observing the surface of a sample using polarized light.

FIG. 2 shows Ca₃Ru₂O₇Photograph of the crystal under normal light.

FIG. 3 shows Ca₃Ru₂O₇Photograph under polarized light.

FIG. 4 shows the color of the domain walls in the same region of the planes CS1 and CS2 parallel to the polarization direction of polarized light as compared to the color rotated by 90 degrees.

In the figure:

which indicates the direction of the crystal lattice of the crystal,

indicating the polarization direction of the polarized optical electric field component,

indicating the direction of incidence of polarized light.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples. The objects, aspects and advantages of the present invention will become more apparent from the following description. It should be understood that the described embodiments are preferred embodiments of the invention, and not all embodiments.

In the manner shown in FIG. 1, a representative non-centrosymmetric crystal Ca is₃Ru₂O₇The crystal is horizontally placed under an epi-microscope, the ab surface of the crystal is kept vertical to the incident direction of polarized light, the color and the stripes of the surface of the crystal are observed, and the crystal is horizontally rotated to enable the direction of the stripes to be consistent with the polarization direction of the polarized light.

For crystals in which domains are present, two different colors can be observed on the surface. As shown in fig. 3, two colors correspond to two domain regions, respectively, and the lattice major axis is in the direction along the domain wall and in the direction perpendicular to the domain wall.

As seen from a comparison of fig. 2 and 3, the spatial distribution of the crystal domains can be effectively determined by using the polarized light reflection.

And (3) dissociating the crystal in the vertical c direction to obtain two dissociation planes CS1 and CS2, selecting corresponding regions of the cleavage planes CS1 and CS2, rotating CS1 and CS2 clockwise by 90 degrees at the same time, and recording the colors CS1_90deg and CS2_90deg of the same region at the moment, as shown in FIG. 4. By color comparison, the orientation of the crystal lattice in different crystal domain regions can be determined.

Wherein the color difference of the crystal domains rotated by 90DEG is derived from the dielectric constant tensor of the material anisotropy

The intensity of the corresponding reflected light at different wavelengths is therefore

Wherein

For reflectivity, θ is the angle between the polarized optoelectronic field component and the principal axis of the crystal as shown in FIG. 1. The color difference of the corresponding unequivalent cleavage planes CS1 and CS2 results from the difference in the energy bands of the two semi-infinite crystals.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the scope of the present invention, and it is obvious that any person skilled in the art can easily conceive of alternative or modified embodiments based on the above embodiments and these should be covered by the present invention.

Claims

1. A method for determining the domain space distribution and the lattice orientation of a non-centrosymmetric crystal is characterized in that:

And imaging by utilizing the space distribution of the crystal domains of the polarized light reflection non-centrosymmetric crystal, then carrying out cleavage and determining the orientation of the crystal lattice.

2. The method for determining the spatial distribution of the domains and the orientation of the crystal lattice of a non-centrosymmetric crystal according to claim 1, wherein:

when the spatial distribution of crystal domains is imaged, a measured non-centrosymmetric crystal is horizontally placed under an epi-microscope, the ab surface of the crystal is kept to be perpendicular to incident light, the positions of a polarizer and an analyzer are fixed, the polarizer and the analyzer are kept to be perpendicular, the position of the crystal is horizontally rotated and adjusted, the color of the surface of the crystal can be seen to change correspondingly along with the change of the position of the crystal, when color stripes are seen on the surface of the crystal, different color regions correspond to different crystal domains, the boundaries of the stripes are domain walls, and the directions of the parallel boundaries and the vertical boundaries correspond to two main axes of crystal lattices respectively.

3. The method for determining the spatial distribution of the domains and the orientation of the crystal lattice of a non-centrosymmetric crystal according to claim 1, wherein:

when cleavage observation is carried out, the crystal is cleaved in a direction perpendicular to the c direction to obtain two corresponding non-equivalent cleavage planes CS1 and CS2, the position of the cleaved crystal is adjusted to a state that a domain wall is parallel to the polarization direction, the same region corresponding to the cleavage planes CS1 and CS2 is observed, the cleavage planes CS1 and CS2 and crystal domains rotated by 90 degrees respectively present 4 different colors, and the lattice orientation of the corresponding region can be directly deduced according to the 4 colors.