JPWO2017154450A1 - Identification method of metal oxide - Google Patents

Abstract

The method for identifying a metal oxide includes an identification step for comparing the analysis result of the reference sample analysis step and the analysis result of the measurement sample analysis step, and identifying the measurement sample with respect to the reference sample in the identification step, (A) The coincidence of the band gap of the reference sample and the band gap of the measurement sample, (B) the coincidence of the total density of the electron trap of the reference sample and the total density of the electron trap of the measurement sample, and (C) the reference sample The density coefficient obtained by multiplying one or both of the degree of coincidence of the density electron trap density energy distribution and the density electron trap density energy distribution of the measurement sample.

Description

  The present invention relates to a method for identifying a metal oxide. This application claims priority on March 10, 2016 based on Japanese Patent Application No. 2006-046888 for which it applied to Japan, and uses the content here.

  The composition of the sample, the crystal structure, the electronic state, the surface structure including the particle size, the specific surface area, and the like greatly affect the physical properties and characteristics of the sample. Therefore, if the sample is not sufficiently identified, the reliability of the measurement result is lowered. That is, the identification of the sample is important, and means for appropriately identifying the sample is required.

For example, when the sample is an organic compound, the sample is identified based on the results of structural analysis such as elemental analysis and nuclear magnetic resonance (NMR).
On the other hand, when the sample is a metal oxide or the like, the composition and structure are analyzed using X-ray diffraction (XRD), and the metal oxide is identified by comparison with a standard sample (for example, patents) Reference 1).

  On the other hand, metal oxides are used for various applications such as photocatalysts, catalyst carriers, pigments, etc., and it cannot be said that the identification of a sample is sufficient only by specifying the bulk composition and structure. Therefore, for example, even with metal oxides having the same composition and the same structure, the physical properties such as catalyst characteristics are often different. This is because the contribution to the physical properties of the surface structure including the particle size and specific surface area of the sample is large.

  Therefore, as a means for measuring the particle size and specific surface area of a sample, a specific surface area measurement method (JIS 8830: 2013) by gas adsorption on powder is known.

JP 2014-52223 A

  However, even if the specific surface area of the powder or the like is specified, it is impossible to determine the influence of the electronic state on the surface, the arrangement of atoms, and the like. For this reason, for example, even slight differences such as product lots, how they were manufactured, and what kind of processing were performed could not be identified, and it could not be said to be sufficient as a sample identification means.

  This invention is made | formed in view of the said situation, and it aims at obtaining the identification method of the metal oxide which can determine the slight difference of a sample, and the evaluation method of a sample.

The inventors of the present invention have information on the electronic state due to the composition, structure, etc. that can be specified by the band gap, etc., information on the electronic state on the sample surface that can be specified by the total density of the electron trap and the energy distribution of the electron trap density, etc. As a result, a metal oxide identification method and a sample evaluation method that can determine even a slight difference in the sample were found.
That is, the present invention has the following configuration.

(1) A method for identifying a metal oxide according to one embodiment of the present invention includes a band gap of a reference sample having a metal oxide, and one or both of a total density of electron traps and an energy distribution of the electron trap density of the reference sample. A measurement sample for measuring a reference sample analysis step for measuring, a band gap of the measurement sample having a metal oxide, and / or one or both of a total density of electron traps and an energy distribution of the electron trap density of the measurement sample An analysis step, and an identification step for comparing the analysis result of the reference sample analysis step and the analysis result of the measurement sample analysis step, and (A) reference sample identification of the measurement sample with respect to the reference sample in the identification step (B) The total density of the electron trap of the reference sample and the total density of the electron trap of the measurement sample with respect to the degree of coincidence between the band gap of the sample and the band gap of the measurement sample Done by degree of matching (C) and a reference matched coefficients obtained by multiplication of one or both of the degree of matching energy distribution and the energy distribution of the electron trap density of the measurement sample of the electron trap density of the sample.

(2) In the method for identifying a metal oxide according to (1), in the reference sample analysis step and the measurement sample analysis step, the total density of electron traps and the energy distribution of the electron trap density of the reference sample and the measurement sample Both are measured, and the identification of the measurement sample with respect to the reference sample in the identification step is performed. (A) The degree of coincidence between the band gap of the reference sample and the band gap of the measurement sample, (B) The total density of the electron trap of the reference sample and the measurement sample The coincidence obtained by multiplying the coincidence of the total density of the electron traps and (C) the coincidence of the energy distribution of the electron trap density of the reference sample and the energy distribution of the electron trap density of the measurement sample. You may carry out by a coefficient.

(3) In the identification step in the method for identifying a metal oxide according to any one of (1) and (2) above, if the coincidence coefficient is greater than 0.3, the reference sample and the measurement sample coincide with each other You may judge.

(4) In the method for identifying a metal oxide according to any one of the above (1) to (3), the energy distribution of the electron trap density is determined to be near red in an atmosphere in which an electron donor is present. Irradiating the reference sample or the measurement sample with continuous light that continuously changes from the long wavelength side to the short wavelength side of outside light, visible light, and ultraviolet light, and the modulated light of a certain wavelength, the reference sample or the You may measure based on the photoacoustic signal detected from the measurement sample.

(5) In the method for identifying a metal oxide according to any one of (1) to (4), the reference sample and the measurement sample are titanium oxide, tungsten oxide, zinc oxide, strontium titanate, and these. It may be at least one selected from the group consisting of those doped with different elements.

It is the energy diagram which showed typically the level by which an electron is trapped. It is the cross-sectional schematic diagram which showed the photoacoustic spectroscopy method typically. It is the figure which showed typically the energy change which arises when a sample is irradiated with modulated light and continuous light. The position (band gap) of the lower end of the conduction band of the four samples obtained in Reference Example 1 and the energy distribution of the electron trap density are shown. The identification result of the metal oxide in Example 1 is shown.

  The configuration of the embodiment of the present invention will be described below. The present invention can be implemented with appropriate modifications without departing from the scope of the invention.

  The method for identifying a metal oxide according to one embodiment of the present invention includes a reference sample analysis step, a measurement sample analysis step, and an identification step.

(Standard sample analysis process, measurement sample analysis process)
In the reference sample analysis step and the measurement sample analysis step, the band gap of the sample having a metal oxide and one or both of the total electron trap density and the electron trap density energy distribution of the sample are measured. The reference sample analysis step and the measurement sample analysis step differ only in whether the object to be measured is a reference sample to be a reference or a measurement sample to be analyzed.

  The band gap measured in the reference sample analysis step and the measurement sample analysis step, the total electron trap density of the sample, and the energy distribution of the electron trap density are roughly classified into two. The band gap is measured mainly from the crystal structure of the sample, and does not depend on the size or shape of the sample. On the other hand, the total density of the electron traps of the sample and the energy distribution of the electron trap density are measured mainly from the surface structure of the sample and are affected by the size, shape, surface state, etc. of the sample. By measuring the information derived from the crystal structure and the information derived from the surface structure, the analysis accuracy can be improved.

As the reference sample and the measurement sample, metal oxides such as titanium oxide, tungsten oxide, zinc oxide, and strontium titanate can be used.
In order to identify the measurement sample from the degree of coincidence with the reference sample, in principle, the same material type is used for the reference sample and the measurement sample. On the other hand, the reference sample and the measurement sample may be different, for example, when the measurement sample cannot be clearly identified.

  As the metal oxide used for the reference sample and the measurement sample, it is preferable to use at least one selected from the group consisting of titanium oxide, tungsten oxide, zinc oxide, strontium titanate and those doped with different elements. As the dissimilar metal, Sr, Cr, V, Mn, Fe, Co, Ni, Zn or the like can be used. These material types are generally used as photocatalysts. Therefore, it is very useful to identify these substances including electronic states in the surface structure.

"Measurement of band gap"
The measurement of the band gap of a sample is performed using well-known methods, such as a diffuse reflection spectrum method and photoacoustic spectroscopy (PAS), for example.

Photoacoustic spectroscopy is particularly preferable because it is not affected by light scattering or the like and can also measure powder samples and biological samples.
Photoacoustic spectroscopy is a method in which a sample is irradiated with modulated light and a volume change caused by periodic heat generation / release generated in the sample is detected as a sound wave. Here, modulated light refers to light whose intensity changes periodically. As an example of the modulated light, there is intermittent light to which light having a constant frequency is supplied intermittently.

The heat generation / release of the sample occurs when the light-absorbed sample is de-excited. Further, the volume change caused by heat generation / release occurs when the sample expands or contracts due to heat. By detecting sound waves generated from the sample, various information such as an absorption spectrum of the sample can be measured.

“Measurement of total density of electron traps”
The total density of the electron trap of the sample is measured by, for example, double-excitation photoacoustic spectroscopy (Double-beam PAS: DB-PAS), photochemical method using methylviologen (S. Ikeda, N. Sugiyama, S.-y). Murakami, H. Konamimi, Y. Kera, H. Noguchi, K. Uosaki, T. Torimoto, and B. Ohtani, Phys. Chem. Chem. Do.

  Here, the electron trap means a level at which excited electrons are trapped. In other words, it is a level that exists between the valence band and the conduction band, and such an electron trap is located in a part different from the ideal crystal structure such as crystal lattice defects and a special reconstruction structure of the surface. It is considered that the level is due. Therefore, measuring the total density of electron traps means the density of crystal lattice defects and surface specific structures as a substance. The crystal lattice defect depends on the mass of the sample, and the surface specific structure depends on the specific surface area. Therefore, in a powder sample except a single crystal, most of the electron traps are caused by the surface-specific structure, and the analysis of the electron trap strongly reflects the surface state of the sample. The “surface specific structure” means a portion different from an ideal internal structure of the crystal such as a surface restructure.

The ability to measure the total density of electron traps, that is, the density of crystal lattice defects and surface specific structures, has the following meaning.
The photocatalytic reaction is widely applied, but there are many unclear points about the details of its action. In particular, there are many unclear points regarding the reaction kinetics, and it is considered that the reaction is mainly caused by the reaction substrate in which excited electrons and holes are adsorbed on the surface, the recombination of electrons and holes, and the like. Since each of these reactions is considered to be related to surface specific structures and crystal lattice defects, the ability to evaluate them qualitatively and quantitatively has great significance for understanding photocatalytic reactions.

Double-excitation photoacoustic spectroscopy (Double-beam PAS: DB-PAS) irradiates modulated light while continuously irradiating light with a wavelength that causes a photoreaction, thereby aging the sample accompanying the photoreaction. Change information and total electron trap density information. The continuous light irradiated on the sample is, for example, high energy light of 300 nm to 400 nm. Also, the modulated light having a certain wavelength is irradiated onto the sample simultaneously with the continuous light.
In double excitation photoacoustic spectroscopy, an electron trap is measured as an atom having a different valence in a sample.

  The principle of measuring the total density of electron traps in the photocatalytic material using double excitation photoacoustic spectroscopy will be specifically described taking as an example the case of using titanium oxide as a sample and methanol vapor as an electron donor.

  When continuous light that causes photoreaction to titanium oxide is irradiated, electrons and holes are generated by the photoreaction. Normally, these electrons and holes recombine, but methanol vapor, which is an electron donor added to the system, and holes react irreversibly. Therefore, the electrons that have lost their destination are trapped by crystal lattice defects and surface-specific structures (in terms of energy, electron traps). The trapped electrons change the tetravalent titanium ions in the titanium oxide into trivalent titanium ions. Since this reaction occurs by being trapped in the electron trap, the total density of the electron trap in the substance can be measured by measuring trivalent titanium ions.

  Measurement of trivalent titanium ions is performed by irradiating light absorbed by the trivalent titanium ions as modulated light. When trivalent titanium ions are present, the trivalent titanium ions absorb and de-excited modulated light, and generate and emit heat. Due to the generated heat, the sample expands or contracts to generate sound waves. That is, by detecting the generated sound wave, trivalent titanium ions can be measured, and thus the total density of the electron trap can be measured.

"Measurement of energy distribution of electron trap density"
The energy distribution of the electron trap density of the powder sample is performed using a method such as reverse double excitation photoacoustic spectroscopy (Reverse Double-beam PAS: RDB-PAS) or an energy decomposition measurement method using a photochemical method.

  Here, the energy distribution of the electron trap density is a distribution of how many electron traps exist in which level. That is, the energy distribution of the electron trap density indicates the distribution of the depth of the level at which the excited electrons are trapped.

  The energy distribution of the electron trap density is an index for evaluating the activity of the substance. Further, the density distribution of the levels at which the excited electrons are trapped is useful as an electron injection characteristic from the dye to the negative electrode in the dye-sensitized solar cell and an indicator of the electrode material in the fuel cell.

For example, as shown in FIG. 1, between the conduction band B _C and the valence band B _V, the level of the excited electrons are trapped (electron traps) there are multiple. Among these electron traps, an electron trap close to the conduction band B _C is a shallow electron trap T _s, and an electron trap far from the conduction band B _C is a deep electron trap T _d .

When the excited electrons are trapped in the electron trap T _s which is close to the conduction band B _C and relatively shallow, the excited electrons are easily thermally excited (detrapped) to the conduction band B _C , and thus this trap -Detrapping extends the life of electrons. On the other hand, if the electrons excited to a relatively deep electron traps T _d away from the conduction band B _C is trapped, the excited electrons remained there without being thermally excited to the conduction band B _C, and a hole Rejoin.

That is, reactions utilizing excited electrons and holes, for example in the photocatalytic reaction, the reaction efficiency, the density of shallow electron traps T _s electron trap is high, deep electron traps T that density of _d is lower becomes higher. Vice versa, a low density of shallow electron traps T _s electron trap, as the density of deep electron traps T _d is high, the reaction efficiency is lowered. In other words, measuring the energy distribution of the electron trap density is an index such as the activity of the substance.

  As a method for measuring the energy distribution of the electron trap density, it is preferable to use the RDB-PAS method. The RDB-PAS method can measure the density distribution of the depth of the electron trap easily and with high accuracy using a small amount of sample.

  Hereinafter, a method for measuring the energy distribution of the electron trap density using the RDB-PAS method will be described.

FIG. 2 is a diagram schematically showing an apparatus for measuring the energy distribution of the electron trap density using the RDB-PAS method.
The RDB-PAS method is a continuous light 1 in which the wavelength continuously changes from the long-wavelength side to the short-wavelength side of near-infrared light, visible light, and ultraviolet light in an atmosphere 4 in which an electron donor is present, and constant. The sample 3 is irradiated with the wavelength-modulated light 2, and the photoacoustic signal from the sample 3 is detected by the microphone 6. Here, the near-infrared light visible light and the ultraviolet light wavelength mean wavelengths of about 1000 nm to 300 nm.
In the reference sample analysis step, the reference sample is used as sample 3, and in the measurement sample analysis step, the measurement sample is used as sample 3.

By irradiating the sample 3 with the continuous light 1 whose wavelength continuously changes from the long wavelength side to the short wavelength side of the visible light wavelength and the modulated light 2 with a constant wavelength, the depth of the electron trap of the sample 3 can be reduced. The density distribution, ie the energy distribution of the electron trap density, is measured.
FIG. 3 is a diagram schematically showing a change in energy generated when the sample is irradiated with the continuous light 1 and the modulated light 2.

The continuous light 1 is continuously irradiated onto the sample 3 while changing the wavelength from the long wavelength side to the short wavelength side of the visible light wavelength. When irradiating the continuous light 1 to the sample 3, electrons from the sample 3 is excited from the valence band B _V to electron trap as indicated by an arrow a. At this time, since the wavelength of the continuous light 1 is changed from the long wavelength side, the energy of the continuous light 1 changes from low energy to high energy. Therefore, when continuous light 1 is irradiated on the specimen 3, the excited electrons will filled in order from the electron traps near the valence band B _V. In other words, in order from deep electron trap T _d, it filled up shallow electron traps T _s.

Irradiation of continuous light 1 causes an energy change indicated by an arrow a in FIG. 3. When the wavelength of continuous light is a long wavelength, it mainly shows a transition to a deep electron trap _Td, and the wavelength of continuous light is a short wavelength. In the case of, the transition to the shallow electron trap T _s is mainly shown.

The sample 3 is also irradiated with modulated light 2 whose intensity is modulated at a constant wavelength. The fixed wavelength can be set in a wavelength region where ions generated by excited electrons absorb.
For example, when the sample 3 is made of titanium oxide, it is possible to set a wavelength region in which trivalent titanium ions generated by excited electrons are absorbed. This absorption wavelength range extends from ultraviolet to infrared wavelengths, and the absorption intensity can be considered to be constant regardless of the depth of electrons trapped in the electron trap.

Therefore, by irradiating the modulated light 2, to excite excited by continuous light 1 to electron trap electrons into the conduction band B _C (arrow b). Heat is generated in the process where electrons excited in the conduction band relax in the electron trap, and the sample 3 expands and contracts due to heat conduction. Since the intensity of the modulated light 2 is modulated, a sound wave is generated with the expansion / contraction synchronized with the modulation frequency.

That is, when the long wavelength continuous light 1 is irradiated, the electrons are excited from the valence band _BV to the deep electron trap _Td . In this case it has been irradiated modulated light 2 simultaneously, electron transitions from deep electron traps T _d to the conduction band B _C. Further, when the wavelength of the continuous light 1 is changed to a short wavelength, excitation of electrons from the valence band B _V to the shallow electron trap T _s is caused by the continuous light 1. At this time, by being irradiated modulated light 2 at the same time, to measure the sound wave that is synchronized with the frequency of the modulated light by the light absorption based on the transition to the conduction band B _C shallow electron traps T _s as the photoacoustic signal it can.

  By irradiating the continuous light 1 whose wavelength continuously changes from the long-wavelength side to the short-wavelength side of the near-infrared light, visible light, and ultraviolet light wavelengths and the constant wavelength modulated light 2, the electron trap of the sample 3 is It is possible to measure the cumulative value of trap density when sequentially filling from the deeper side. Further, by differentiating this, it is possible to obtain the density distribution of the electron trap at each depth as the change amount of the accumulated value.

  Under the condition that the modulated light is lower in intensity than the continuous light, only a small part of the electrons accumulated in the electron trap are excited to the conduction band by the modulated light. When the excited electrons are trapped again in the electron trap, a photoacoustic signal (hereinafter referred to as a PA signal) is generated. The signal intensity is proportional to the amount of trapped electrons.

Since the electron donor has an electron donating property, that is, a hole accepting property, it captures holes generated by light irradiation. Therefore, by performing the treatment in the atmosphere 4 in which the electron donor exists, it is possible to suppress the reaction between the electrons and holes trapped in the electron trap and disappearance.
When the electrons trapped in the electron trap and the electrons trapped in the electron trap disappear, the density of the electron trap cannot be measured accurately. The atmosphere 4 in which the electron donor exists can be realized by surrounding the sample 3 with a closed cell 5 as shown in FIG.

  The electron donor is not particularly limited as long as it can capture holes generated by light irradiation. For example, methanol, ethanol, 2-propanol, triethylamine, trimethylamine, triethanolamine, etc. can be used. Among these, at least one selected from the group consisting of methanol, triethylamine, and triethanolamine is preferable because it can be produced inexpensively and easily.

  As described above, by using the RDB-PAS method, the depth density of the electron trap can be measured easily and accurately with a small amount of sample.

  The energy distribution of the band gap, the total density of electron traps, and the electron trap density of the reference sample and the measurement sample is measured by the procedure as described above.

  Both the total density of the electron trap and the energy distribution of the electron trap density are obtained by measuring information derived from the surface structure. Therefore, only one of the measurements may be performed. From the viewpoint of increasing the final sample identification accuracy, it is preferable to measure all.

(Identification process)
In the identification step, the information on the reference sample and the information on the measurement sample obtained by the procedure as described above is used to identify how much the measurement sample matches the reference sample.

  In the identification step, first, (A) the coincidence between the band gap of the reference sample and the band gap of the measurement sample, (B) the coincidence between the total density of the electron trap of the reference sample and the total density of the electron trap of the measurement sample, (C) The degree of coincidence between the energy distribution shape of the electron trap density of the reference sample and the energy distribution shape of the electron trap density of the measurement sample is obtained.

  Note that, in the reference sample analysis step and the measurement sample analysis step, when either the total density of the electron trap or the energy distribution of the electron trap density is not measured, the degree of coincidence of either one does not need to be measured. Hereinafter, a case where both the degrees of coincidence are used will be described as an example.

“(A) The degree of coincidence between the band gap of the reference sample and the band gap of the measurement sample”
First, the degree of coincidence of band gaps is obtained. The degree of coincidence of the band gap is a band gap ratio. The degree of coincidence of the band gaps is obtained by dividing the band gap of the reference sample to be compared and the band gap of the measurement sample by dividing the smaller energy level difference by the larger one. That is, the band gap coincidence is always obtained as a value of 1 or less.

The band gap coincidence is C _A , the energy level difference having the smaller energy level difference among the band gap of the reference sample and the band gap of the measurement sample is E _gs , and the band gap of the reference sample and the band gap of the measurement sample are If the energy level difference with the larger energy level difference is E _gb , it is expressed as the following general formula (1).
C _A = E _gs / E _gb ≦ 1 (1)

“(B) Agreement between the total density of the electron traps of the reference sample and the total density of the electron traps of the measurement sample”
Next, the degree of coincidence of the total density of the electron traps is obtained. The coincidence of the total density of electron traps is a ratio of the total density of electron traps. The degree of coincidence of the total density of the electron traps is obtained by dividing the total density of the electron traps of the reference sample to be compared and the total density of the electron traps of the measurement sample by dividing the smaller total density of the electron traps by the larger one. That is, the degree of coincidence of the total density of electron traps is always obtained as a value of 1 or less.

The coincidence of the total density of the electron traps is C _B , the total density of the electron traps of the reference sample and the total density of the electron traps of the measurement sample is D _s , and the total density of the electron trap of the reference sample is When the total density of the larger electron trap among the total density and the total density of the electron trap of the measurement sample is D _b , the following general formula (2) is expressed.
C _B = D _s / D _b ≦ 1 (2)

“(C) The degree of coincidence between the energy distribution of the electron trap density of the reference sample and the shape of the energy distribution of the electron trap density of the measurement sample”
Finally, the degree of coincidence of the shape of the energy distribution of the electron trap density is obtained. The degree of coincidence of the shape of the energy distribution of the electron trap density is obtained by least square approximation. Specifically, the square root of the sum of the squares of the differences in each energy, which is minimized by multiplying the higher total electron trap density by a coefficient, is the total density of the lower electron trap density. This is obtained by subtracting this from 1. That is, the coincidence degree of the energy distribution of the electron trap density is always obtained as a value of 1 or less. Here, the degree of coincidence of the energy distribution shape is obtained by the least square approximation method, but the degree of coincidence may be derived by a curve fitting method or the like.

The degree of coincidence of the shape of the energy distribution of the electron trap density is C _C , the total density of the electron trap of the reference sample and the total density of the electron trap of the measurement sample is D _s , Of the total density of the electron trap and the total density of the electron trap of the measurement sample, the total density of the larger electron trap is D _b , the coefficient is x, and the measurement energy range is divided into n measurement intervals. Assuming that the partial density of the electron trap, which is smaller and larger, is d _b and d _s , respectively, an expression based on the least square approximation is expressed as the following general expression (3). Here, σ _n = (xd _b −d _s ) (n is an integer). x is a coefficient obtained so that the difference in partial density at each energy is minimized.

The coincidence coefficient I is obtained using the coincidence C _A of the band gap, the coincidence C _B of the total density of the electron traps, and the coincidence C _C of the energy distribution of the electron trap density obtained by the above procedure.

The coincidence coefficient I is obtained by multiplying the coincidence degree C _A of the band gap, the coincidence degree C _B of the total density of the electron traps, and the coincidence degree C _C of the energy distribution of the electron trap density. That is, it is expressed by I = C _A × C _B × C _C. At this time, each degree of coincidence C _A , C _B, and C _C may be used as m-th power (m is an arbitrary number excluding 0). Identification according to the importance for each degree of coincidence can be performed by raising the degree of coincidence to the power of m.

When either the coincidence C _B of the total density of electron traps or the coincidence C _C of the shape of the energy distribution of the electron trap density is not obtained, it is expressed as I = C _A × C _B or I = C _A × C _C Sometimes it is done.

For example, when titanium oxides manufactured by different manufacturers are compared, the coincidence coefficient I is 0.3 or less (I = C _A × C _B × C _C ≦ 0.3). On the other hand, when the same manufacturer and the same manufacturing method are compared, the coincidence coefficient I is larger than 0.3. Further, when the coincidence coefficient I was independently determined three times for the titanium oxide in one purchased bottle, the coincidence coefficient I was 0.8 or more (I = C _A × C _B × C _C ≧ 0.8). Titanium oxide sealed in one purchased bottle is thought to be made by the same manufacturer, the same manufacturing method, and the same lot.

  As described above, when the metal oxide identification method according to one embodiment of the present invention is used, differences in metal oxide manufacturers, manufacturing methods, manufacturing lots, and the like can be analyzed in detail. That is, even a slight difference in the metal oxide can be quantitatively evaluated by this new index of coincidence coefficient I.

(Reference Example 1)
First, four samples were prepared.
Sample 1-1: Anatase-type titanium oxide (TIO-1: see Catalysts of the Catalysis Society)
Sample 1-2: Titanium oxide in which anatase type and rutile type are mixed (TIO-11: Catalyst Society of Japan Reference Catalyst), the ratio of anatase type is greater than that in rutile type Sample 1-3: Titanium oxide in which anatase type and rutile type are mixed (TIO-5: Catalytic Society Reference Catalyst), anatase type ratio is less than rutile type Sample 1-4: Rutile type titanium oxide (TIO-6: Reference Catalyst of Catalytic Society)

  The band gap, total electron trap density, and electron trap density energy distribution of these four samples were measured.

  The band gap was measured using the photoacoustic spectroscopy (PAS) method (normal method / single beam) using the same apparatus as RDB-PAS. Specifically, the sample holder was filled with sample powder, methanol vapor saturated argon gas was circulated in the cell, and then sealed. Intermittent light (modulated light) from a xenon lamp (Spectral Products ASB-XE-175) and a chopper (NF circuit design block 5584A light chopper) equipped with a diffraction grating spectrometer (Spectral Products CM110) is swept from a wavelength of 650 nm to 350 nm. At each wavelength, a photoacoustic signal from a microphone (Panasonic small electret condenser microphone WM-61A) was detected using a lock-in amplifier (NF circuit design block LI5630 digital lock-in amplifier). The obtained spectrum was measured by the procedure of correcting the light source intensity with the spectrum of the graphite sample measured under the same conditions.

The total density of the electron trap and the energy distribution of the electron trap density were measured using the RDB-PAS method. Specifically, continuous light that changes from a long wavelength of 650 nm to a short wavelength of 350 nm and modulated light having a wavelength (625 nm) absorbed by trivalent titanium ions are produced by a light mixing type quartz fiber light guide (Mortex 1000S-UV3). After mixing, each sample was irradiated under an atmosphere of methanol vapor. Continuous light was obtained using the xenon lamp and the diffraction grating spectrometer. The frequency of intensity modulation of the modulated light was 80 Hz, and was obtained using a light emitting diode (Luxeon LXHL-ND98) and (NF circuit design block DF1906 digital function generator).
A sound wave generated at this time was detected by a lock-in amplifier from a photoacoustic signal (hereinafter referred to as a PA signal) from a microphone.

  The PA signal was plotted against the continuous light wavelength to obtain an inverted double excitation photoacoustic spectrum (hereinafter referred to as RDB-PA spectrum). By differentiating the obtained RDB-PA spectrum from the long wavelength side to the short wavelength side as a function of wavelength, an energy distribution of electron trap density was obtained. The total energy distribution is the total density of electron traps.

  FIG. 4 shows the positions of the lower ends of the conduction bands (band gaps) of the four samples obtained in Example 1 and the energy distribution of the electron trap density. The vertical axis is energy based on the upper end of the valence band, and the horizontal axis is electron trap density. In the figure, the surface area of the sample per unit mass of each sample is shown.

  As shown in FIG. 4, reflecting the fact that anatase-type titanium oxide and rutile-type titanium oxide have band gaps of 3.2 eV and 3.0 eV, respectively, the conduction band bottom position changes, It can be seen that the trap density distribution varies from sample to sample.

Example 1
Four samples were then prepared.
Sample 1-2: Sample 1-2 in Reference Example 1
Sample 2-1: Titanium oxide in which anatase type and rutile type are mixed (FP-6: manufactured by Showa Denko Ceramics), the ratio of anatase type is greater than that in rutile type. Sample 2-2: oxidation in which anatase type and rutile type are mixed Titanium (TIO-4: catalyst catalyst reference catalyst), the ratio of anatase type is higher than that of rutile type Sample 2-3: titanium oxide mixed with anatase type and rutile type (P25: manufactured by Evonik (Aerosil Japan)), anatase type Is more than the rutile type

The band gap, total electron trap density, and electron trap density energy distribution of these four samples were measured. The measurement method was the same as in Reference Example 1. The band gap coincidence C _A , the electron trap total density coincidence C _B , and the electron trap density energy distribution coincidence C _C were obtained and multiplied to obtain the coincidence coefficient I. . The results are shown in FIG.

  The Catalytic Society Reference Catalyst is distributed as a reference sample by the Catalytic Society of Japan, and the certified name of the Catalytic Society is given to the titanium oxide of each company. The correspondence between each company's titanium oxide and the reference catalyst is officially displayed only in the company name. It is common knowledge that Sample 1-2 and Sample 2-1 have the same brand name P25, and are considered to be separate lot products of the same manufacturing method. Sample 2-2 and sample 2-3 are different lot products of the same brand, that is, almost the same manufacturing process.

  When FIG. 5 is seen, the high coincidence coefficient I is obtained between the sample 2-2 and the sample 2-3 and between the sample 1-2 and the sample 2-1. That is, it can be seen that the difference in titanium oxide can be determined with high accuracy. In addition, the same result was obtained even if the same examination was performed using 20 or more types of commercial products.

DESCRIPTION OF SYMBOLS 1 ... Continuous light, 2 ... Modulated light, 3 ... Sample, 4 ... Atmosphere where electron donor exists, 5 ... Sealed cell, 6 ... Microphone

Claims (8)

A reference sample analysis step of measuring a band gap of a reference sample having a metal oxide, and one or both of the total electron trap density and the electron trap density energy distribution of the reference sample;
A measurement sample analysis step for measuring the band gap of the measurement sample having a metal oxide, and one or both of the total density of electron traps and the energy distribution of the electron trap density of the measurement sample;
An identification step for comparing the analysis result of the reference sample analysis step and the analysis result of the measurement sample analysis step,
The identification of the measurement sample with respect to the reference sample in the identification step is performed according to (A) the degree of coincidence between the band gap of the reference sample and the band gap of the measurement sample, and (B) the total density of the electron traps of the reference sample and the electron trap of the measurement sample. Identification of metal oxide based on the coincidence coefficient obtained by multiplying the coincidence of the total density, (C) the energy distribution of the electron trap density of the reference sample, and the coincidence of the energy distribution of the electron trap density of the measurement sample. Method. In the reference sample analysis step and the measurement sample analysis step, both the total density of the electron trap and the energy distribution of the electron trap density of the reference sample and the measurement sample are measured,
In the identification step, the measurement sample is identified with respect to the reference sample by (A) the degree of coincidence between the band gap of the reference sample and the band gap of the measurement sample, (B) the total density of the electron traps of the reference sample and the total of the electron traps of the measurement sample. And (C) the coincidence coefficient obtained by multiplying the coincidence of the energy distribution of the electron trap density of the reference sample and the coincidence of the energy distribution of the electron trap density of the measurement sample. 2. The method for identifying a metal oxide according to 1.   The method for identifying a metal oxide according to claim 1, wherein, in the identification step, if the coincidence coefficient is greater than 0.3, it is determined that the reference sample and the measurement sample coincide with each other.   Energy distribution of the electron trap density, continuous light in which the wavelength continuously changes from the long wavelength side to the short wavelength side of the near infrared light, visible light and ultraviolet light wavelengths in an atmosphere in which an electron donor exists, The metal oxide identification method according to claim 1, wherein the reference sample or the measurement sample is irradiated with modulated light having a predetermined wavelength, and measurement is performed based on a photoacoustic signal detected from the reference sample or the measurement sample.   The reference sample and the measurement sample are at least one selected from the group consisting of titanium oxide, tungsten oxide, zinc oxide, strontium titanate, and those doped with a different element. Identification method of metal oxide.   3. The method for identifying a metal oxide according to claim 2, wherein, in the identification step, if the coincidence coefficient is greater than 0.3, it is determined that the reference sample and the measurement sample coincide with each other.   Energy distribution of the electron trap density, continuous light in which the wavelength continuously changes from the long wavelength side to the short wavelength side of the near infrared light, visible light and ultraviolet light wavelengths in an atmosphere in which an electron donor exists, The metal oxide identification method according to claim 2, wherein the reference sample or the measurement sample is irradiated with modulated light having a predetermined wavelength, and measurement is performed based on a photoacoustic signal detected from the reference sample or the measurement sample.   3. The reference sample and the measurement sample are at least one selected from the group consisting of titanium oxide, tungsten oxide, zinc oxide, strontium titanate, and those doped with a different element. Identification method of metal oxide.

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