Spectra Of Mixed Crystals Research Articles

Effect of isotope disorder on the Raman spectra of cubic boron arsenide

Boron arsenide (c-BAs) is at the forefront of research on ultrahigh thermal conductivity materials. We present a Raman scattering study of isotopically tailored cubic boron arsenide single crystals for 11 isotopic compositions spanning the range from nearly pure c-$^{10}$BAs to nearly pure c-$^{11}$BAs. Our results provide insights on the effects of strong mass disorder on optical phonons and the appearance of two-mode behavior in the Raman spectra of mixed crystals. Strong isotope disorder also relaxes the one-phonon Raman selection rules, resulting in disorder-activated Raman scattering by acoustic phonons.

Clustering/anticlustering effects on the GeSi Raman spectra at moderate (Ge,Si) contents: Percolation scheme vs. ab initio calculations

We test a presumed ability behind the phenomenological percolation scheme used for the basic description of the multi-mode Raman spectra of mixed crystals at one dimension along the linear chain approximation, to determine, via the Raman intensities, the nature of the atom substitution, as to whether this is random or due to local clustering/anticlustering. For doing so, we focus on the model percolation-type GeySi1−y system characterized by six oscillators {1×(Ge−Ge),3×(Ge−Si),2×(Si−Si)} and place the study around the critical compositions y ∼ (0.16, 0.71, and 0.84) corresponding to nearly matching of intensities between the like Raman modes from a given multiplet (Ge−Si triplet or Si−Si doublet). The interplay between the GeySi1−y Raman intensities predicted by the percolation scheme depending on a suitable order parameter κ of local clustering/anticlustering is found to be consistent with ab initio calculations of the GeySi1−y Raman spectra done with the Ab Initio Modeling PROgram code using large (64-, 216-, and 512-atoms) disordered cubic supercells matching the required (y,κ) values. The actual “percolation vs. ab initio” comparative insight at moderate/dilute-(Ge,Si) limits, with an emphasis on the κ-induced intra-bond transfer of oscillator strength, extends a pioneering one earlier achieved at an intermediate composition (y ∼ 0.50) by using small (32-atom) supercells [O. Pagès et al., J. Appl. Phys. 114, 033513 (2013)], mainly concerned with the inter-bond transfer of oscillator strength, providing altogether a complete picture.

The stochastic model for ternary and quaternary alloys: Application of the Bernoulli relation to the phonon spectra of mixed crystals

To understand and interpret the experimental data on the phonon spectra of the solid solutions, it is necessary to describe mathematically the non-regular distribution of atoms in their lattices. It appears that such description is possible in case of the strongly stochastically homogenous distribution which requires a great number of atoms and very carefully mixed alloys. These conditions are generally fulfilled in case of high quality homogenous semiconductor solid solutions of the III–V and II–VI semiconductor compounds. In this case, we can use the Bernoulli relation describing probability of the occurrence of one n equivalent event which can be applied, to the probability of finding one from n configurations in the solid solution lattice. The results described in this paper for ternary HgCdTe and GaAsP as well as quaternary ZnCdHgTe can provide an affirmative answer to the question: whether stochastic geometry, e.g., the Bernoulli relation, is enough to describe the observed phonon spectra.

Optical absorption behavior of Tl+ DOPED Rb(Br1–x I x ) system

The optical absorption behavior of Tl+ doped Rb(Br1–x I x ) mixed crystals (with x = 0.00, 0.05, and 0.10) grown under vacuum by slow cooling from the melt has been studied. Absorption spectra of the mixed crystals recorded at room temperature showed that the characteristic A-absorption band of Tl+ ions in the Rb(Br1–x I x ) system (0.1 mol. %) with x = 0.00 (i.e., RbBr:Tl+) broadened with the iodine content towards the low energy side. Changes in the absorption spectra of the mixed crystals are due to creation of some complex centers involving Tl+, Br–, and I- ions with energy levels inside the band gap while forming the mixed crystal. The absorption spectra of gamma-irradiated mixed crystals showed the F-band, which shifted towards the low energy side due to the existence of iodine ions in the mixed crystals.

Percolation versus cluster models for multimode vibration spectra of mixed crystals: GaAsP as a case study

We reexamine the phonon mode behavior of GaAsP, the leading system among those alloys that exhibit ``anomalous'' vibration spectra of the one-$\text{bond}\ensuremath{\rightarrow}\text{multimode}$ type, the sign of a far-from-random substitution if we refer to the 1-$\text{bond}\ensuremath{\rightarrow}4$-mode cluster model (microscopic insight), which has been accepted through use. In fact, we show that the phonon behavior of GaAsP obeys a basic version of the 1-$\text{bond}\ensuremath{\rightarrow}2$-mode percolation model (mesoscopic insight), just as the phonon behaviors of InGaAs, InGaP, and ZnTeSe [O. Pag\`es et al., Phys. Rev. B 77, 125208 (2008)], the leading systems representing the three admitted variants of the ``nominal'' 1-$\text{bond}\ensuremath{\rightarrow}1$-mode type for random alloys as covered by the modified random element isodisplacement model (macroscopic insight). With this, GaAsP and its like are rehabilitated as random alloys in principle, and further, the percolation paradigm generalizes to all types and subtypes of the traditional classification of phonon mode behavior of semiconductor alloys, based on the virtual crystal approximation. The discussion is supported by phenomenological modeling of representative Raman and infrared-reflectivity spectra of GaAsP taken from the literature via the percolation model, ab initio insight into the phonon mode behavior of basic impurity motifs, and existing experimental/ab initio bond length data.

Vibrational behavior of [formula omitted] guest ions included in K 2Me(CrO 4) 2·2H 2O ( Me = Co, Ni) and crystal structures of K 2Me(CrO 4) 2·2H 2O ( Me = Co, Ni)

Crystal structures of the isotypic compounds K 2Co(CrO 4) 2·2H 2O and K 2Ni(CrO 4) 2·2H 2O were refined from X-ray powder diffraction data (triclinic, space group P 1 ¯ , Z = 1, a = 6.432(1)/6.425(1), b = 7.396(1)/7.355(1), c = 5.643(1)/5.619(1) Å, α = 96.61(1)/96.78(2), β = 106.64(1)/106.60(1), γ = 109.75(1)/109.84(1)°, V = 235.3/232.4 Å 3, R wp = 8.22/9.27% for the Co/Ni-compound). The structures are composed of Me 2+O 4(H 2O) 2 octahedra and CrO 4 groups forming kröhnkite-type octahedral–tetrahedral infinite chains which are linked by the potassium ions to layers and further to a three-dimensional framework. The proposed hydrogen-bonding scheme provides further linkage within the chains as well as between neighboring layers. The structures belong to ‘type A’ of the large group of compounds containing kröhnkite-type chains. Vibrational spectra (infrared and Raman) of K 2 Me(CrO 4) 2·2H 2O ( Me = Co, Ni) as well as infrared spectra of mixed crystals K 2 Me(CrO 4) 2− x (SO 4) x ·2H 2O (where x are approximately 0.05, 0.1 and 0.2 for the cobalt matrix, and 0.02, 0.1 and 0.15 for the nickel one) are presented and discussed with respect to the normal vibrations of the tetrahedral ions and the hydrogen bond system. The spectroscopic experiments reveal that ν 1 of the CrO 4 2 - ions appear at higher frequencies than two of the three components of ν 3, i.e. ν 1 > ν 3b ( ν 3a, ν 3b and ν 3c are site-group components of ν 3, ν 3c being the lowest wavenumbered component). The SO 4 2 - guest ions matrix-isolated in both matrices exhibit three infrared bands corresponding to the three site-group components of the asymmetric stretching and bending modes in good agreement with the low site symmetry of the CrO 4 2 - host ions ( C 1 site symmetry). The values of Δ ν 3 (site-group splitting) are larger than those of Δ ν 4 (84 and 10 cm −1 in the cobalt matrix, and 88 and 8 cm −1 in the nickel one, respectively), thus indicating a stronger distortion of the SO 4 2 - guest ions with respect to the S–O bond lengths than to the O–S–O bond angles. The influence of the SO 4 2 - guest ion concentrations on the infrared band positions is also commented. Matrix-isolated in K 2 Me(CrO 4) 2·2H 2O ( Me = Co, Ni) sulfate ions exhibit a stronger degree of energetic distortion than that of the same ions included in K 2 Me(CrO 4) 2·2H 2O ( Me = Mg, Zn, Cd) as deduced from the values of Δ ν 3 and Δ ν max (the difference between the highest and the lowest wavenumbered components of the stretching modes). These spectroscopic findings are owing to the electronic configuration of the Me 2+ ions (for example, Δ ν 3 and Δ ν max of SO 4 2 - ions matrix-isolated in K 2Zn(CrO 4) 2·2H 2O have values of 73 and 163 cm −1, and 88 and 173 cm −1 in K 2Ni(CrO 4) 2·2H 2O, respectively). Metal ions with CFSE ≠ 0 (crystal field stabilization energy, Co 2+ and Ni 2+) are more resistant to angular deformations, i.e. to bond angle changes in the respective MeO 6 octahedra, thus facilitating the distortion of the adjacent tetrahedra as compared to those with CFSE = 0 (Mg 2+, Zn 2+, Cd 2+). The influence of the metal ion nature ( Me 2+ and Me +) on the values of Δ ν 3 and Δ ν max of matrix-isolated SO 4 2 - ions in different matrices with kröhnkite-type octahedral–tetrahedral chains – chromates K 2 Me(CrO 4) 2·2H 2O ( Me = Mg, Co, Ni, Zn, Cd) and selenates Na 2 Me(SeO 4) 2·2H 2O ( Me = Co, Ni, Zn, Cd) is analyzed. SO 4 2 - guest ions included in chromate matrices K 2 Me(CrO 4) 2·2H 2O ( Me = Co, Ni, Cd) are remarkably less distorted than in selenate ones Na 2 Me(SeO 4) 2·2H 2O ( Me = Co, Ni, Cd) as deduced from the values of Δ ν 3 and Δ ν max owing to weaker static fields caused by the larger K + ions as compared to that caused by the smaller Na + ions. The strength of the hydrogen bonds in the title compounds, i.e. the frequencies of ν OD (matrix-isolated HDO molecules) is discussed in terms of hydrogen bond distances O w···O, proton acceptor capacity of the oxygen atoms deduced from their bond-valence sums and Me–OH 2 interactions ( synergetic effect).

Vibrational behavior of [formula omitted] ions included in K 2Zn(CrO 4) 2·2H 2O and crystal structure of K 2Zn(CrO 4) 2·2H 2O: A new structure type containing kröhnkite-type chains

The crystal structure of K 2Zn(CrO 4) 2·2H 2O was determined from single-crystal X-ray diffraction data (monoclinic, space group C2/ c, a = 15.046(2), b = 5.664(1), c = 12.333(2) Å, β = 116.58(1)°, V = 939.9(3) Å 3, Z = 4, R 1 = 0.027 for 2405 F o > 4 σ( F o) and 78 variables). The structure is built up from ZnO 4(H 2O) 2 and CrO 4 groups forming kröhnkite-type infinite octahedral-tetrahedral chains which are linked by K + cations to layers and further to a three-dimensional framework. Hydrogen bonds are located within the chains as well as further interlink adjacent layers. Among the large group of compounds containing kröhnkite-type chains, K 2Zn(CrO 4) 2·2H 2O represents a new structure type, designated ‘type H’, with closest relationships to the triclinic ‘type A’ compounds. Vibrational spectra (infrared and Raman) of K 2Zn(CrO 4) 2·2H 2O as well as infrared spectra of mixed crystals K 2Zn(CrO 4) 2− x (SO 4) x ·2H 2O (where x is approximately 0.05, 0.15 and 0.30) are presented and discussed in the region of the Cr–O and S–O stretching modes, respectively. The SO 4 2 - guest ions matrix-isolated in K 2Zn(CrO 4) 2·2H 2O exhibit three infrared bands for ν 3 and one band for ν 1 as expected due to the low site symmetry C 1 of the host CrO 4 2 - ions. When the larger CrO 4 2 - ions are replaced by the smaller SO 4 2 - ions the mean values of the asymmetric stretches of the guest ions are shifted to lower frequencies as compared to that of the same ions in K 2Zn(SO 4) 2·2H 2O (decreasing repulsion potential at the lattice sites). The energetic distortion of the SO 4 2 - guest ions included in K 2 Me(CrO 4) 2·2H 2O ( Me = Mg, Cd, Zn) as deduced from the values of Δ ν 3 (site-group splitting) and Δ ν max (the difference between the highest and the lowest wavenumbered components of the stretching modes) decrease in the order Zn > Cd > Mg as a result of the decreasing covalency of the respective Me–O bonds in the same order (for example, Δ ν 3 have values of 73, 58 and 36 cm −1, respectively). The infrared spectroscopic experiments show that the SO 4 2 - guest ions included in the chromates are considerably less distorted than in the selenates with kröhnkite-type chains Na 2 Me(SeO 4) 2·2H 2O ( Me = Cd, Zn) due to both the weaker static field caused by the larger K + ions as compared to that caused by the smaller Na + ions and the smaller unit-cell volumes of the chromate compounds (Δ ν 3 and Δ ν max of SO 4 2 - guest ions have values of 73 and 163 cm −1 in K 2Zn(CrO 4) 2·2H 2O and 116 and 207 cm −1 in Na 2Zn(SeO 4) 2·2H 2O).

Identification of the La6F37 cubooctahedral clusters in mixed crystals (BaF2)1 − x (LaF3) x by the electron paramagnetic resonance method

The electron paramagnetic resonance (EPR) spectra of mixed crystals (BaF2)1 − x (LaF3) x (x = 0, 0.001, 0.002, 0.005, 0.010, 0.020) doped with Ce3+ ions (0.1%) are investigated at a frequency v ≈ 9.5 GHz in magnetic fields up to 1.45 T at temperatures T = 10 and 15 K. The EPR spectrum of “pure” barium fluoride BaF2 (x = 0) is characterized by a single Ce3+-F− center with tetragonal symmetry (i.e., the O center with g ‖ = 2.601 and g ⊥ = 1.555). For a lanthanum trifluoride concentration x ≠ 0, the spectrum exhibits new lines due to the presence of the clusters containing Ce3+ and La3+ ions. The intensity of EPR signals from the O centers decreases rapidly as the lanthanum trifluoride concentration x increases. The lines attributed to a paramagnetic center with tetragonal symmetry and strongly anisotropic g factors (i.e., the K center with g ‖ = 0.725 and g ⊥ = 2.52) are separated in the complex EPR spectrum with the use of the angular dependence of the EPR signal intensity measured for the samples with x ≥ 0.002. This center is identified as a cubooctahedral cluster of the La6F37 type in which one of the La3+ ions is replaced by the Ce3+ ion.

Influence of thallium doping on scintillation characteristics of mixed KDP/ADP crystals

Crystals of K 1 - x A x DP : Tl (0.1 wt%) were grown. Different fractions of potassium ions in the form of prism and pyramid morphology at x > 0.8 were found. The fluorescence emission (277–282 nm) and excitation (205–210 and 225–230 nm) spectra of mixed crystals doped with thallium were measured. The scintillation light output was determined under excitation by both α - and β -particles.

負イオンマトリックス支援レーザー脱離イオン化質量分析法による中性糖鎖解析 ＩＩ：マトリックス‐塩の相互作用による中性糖鎖の効率的負イオン化

Efficient ionization of neutral oligosaccharides in negative-ion matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was achieved; harmine (7-methoxy-1-methyl-9H-pyrido[3,4-b]indole) was used as a matrix and ammonium chloride was added as a chloride source to generate chlorinated molecules of neutral oligosaccharide. Increasing the molar amount of ammonium chloride gradually increased the ionization efficiency, which was saturated by adding over 2 molar equivalents of ammonium chloride to the matrix. Ionization efficiency increased when the concentration of salt was high. The results of solid phase fluorescence spectra of mixed crystals indicated that harmine was protonated and formed the hydrochloride salt. Results of ultraviolet absorption spectra showed that harmine hydrochloride absorbed ultraviolet laser irradiation from a nitrogen laser (337 nm) more effectively than harmine, and that ionization efficiency of the chlorinated molecule increased. Harmine hydrochloride was the most effective matrix.

Electron Paramagnetic Resonance in Mixed Crystals (BaF[sub 2])[sub 1 – x](LaF[sub 3])[sub x] Activated by Ce[sup 3+] Ions

The electron paramagnetic resonance (EPR) spectra of mixed crystals (BaF2)1−x− y (LaF3)x(CeF3)y (y = 0.001 = 0.1%, x = 0–0.02) are investigated in a magnetic field H‖C4 at a frequency of 9.5 GHz. The angular dependence of the EPR spectrum is measured for the sample with x = 0.02. The lines attributed to Ce3+ impurity centers with tetragonal symmetry and g factors (g ‖ = 0.75, g ⊥ = 2.4) close to those measured for the KY3F10: Ce3+ compound are separated in the complex EPR spectrum. The assumption is made that the aforementioned impurity centers are cubooctahedral clusters of the La6F37 type in which one of the La3+ ions is replaced by the Ce3+ ion.

Percolation effect in the vibrational spectra of mixed crystals with highly contrasted bond stiffness

We present a detailed investigation by Raman spectroscopy of the zone-center longitudinal (LO) and transverse (TO) optical phonons from Zn 1− x Be x Te epilayers with special emphasis on samples with low-medium Be content. On top of the expected ZnTe- and BeTe-like modes, which obey the standard modified-random-element-isodisplacement (MREI) model, we observe an additional BeTe-like mode at intermediate frequency. At medium Be-content (0.2< x<0.61), this extra mode is a real (TO, LO) doublet. We show that its frequency dependence versus x obeys a ‘restricted’ MREI description. On the strength side, it is remarkable that the extra mode grows at the cost of the other BeTe-like mode when x increases; the balance is equilibrated at x∼0.5. At low Be content ( x≤0.2), the Raman response from the extra mode changes in nature; it turns from a restricted MREI-like (TO, LO) doublet into a TO–LO degenerated mode with fixed frequency. One key point is that the latter stays below the local mode of Be in ZnTe. The present results enrich our ZnBeSe-based percolative picture for multimode description in Be–chalcogenide alloys that open the attractive class of mixed crystals with a sharp contrast in the bond stiffness.

Effects of the phase transition in Hg2(Br,I)2 crystals

The effects of the phase transition in Hg2(Br,I)2 crystals have been investigated over a wide range of temperatures by the Raman scattering spectroscopy and X-ray diffraction analysis. The overtones (at the X point of the Brillouin zone boundary) and the fundamental tones (at the center of Brillouin zone) of soft modes are found in the Raman spectra of these crystals and studied in detail. The density of one-phonon states of the soft TA branch manifests itself in the Raman spectra of mixed crystals. The potentialities of the soft-mode spectroscopy are realized in full measure. Analysis of the ratio between intensities of overtones and fundamental tones of the soft modes has demonstrated the applicability of the Landau phenomenological theory of phase transitions. The orthorhombic splitting of the reflections corresponding to the basal plane is revealed in the X-ray diffraction patterns and thoroughly explored. The temperature dependences of the isotropic and shear spontaneous strains are obtained. It is shown that the shear spontaneous strain plays a decisive role. The critical indices are determined and the model of the improper ferroelastic phase transition D 4 17 → D 2 17 in the vicinity of the tricritical point is corroborated.

Temperature‐dependent Raman spectra of mixed crystals of NaNO3–KNO3: evidence for limited solid solutions

The temperature dependence of the Raman spectra of NaNO3–KNO3 was employed to follow structural phase transitions of mixed crystals with different compositions. Solid solutions in the NaNO3 terminal phase behaved like NaNO3 I, solid solutions in the KNO3 terminal phase behaved like KNO3 I and solid solutions in the intermediate phase appeared to be a mixture of NaNO3 I and KNO3 I on the scale of a few tens to hundreds of nanometers. The three different behaviours of the solid solutions below the solidus suggest that NaNO3–KNO3 might well be regarded as a system with limited solid solutions instead of a continuous series of solid solutions. The limited solid solution model seems to be more consistent with the phase diagrams obtained by differential scanning calorimetry. Copyright © 1999 John Wiley & Sons, Ltd.

Temperature-dependent Raman spectra of mixed crystals of NaNO3-KNO3: evidence for limited solid solutions

The temperature dependence of the Raman spectra of NaNO3–KNO3 was employed to follow structural phase transitions of mixed crystals with different compositions. Solid solutions in the NaNO3 terminal phase behaved like NaNO3 I, solid solutions in the KNO3 terminal phase behaved like KNO3 I and solid solutions in the intermediate phase appeared to be a mixture of NaNO3 I and KNO3 I on the scale of a few tens to hundreds of nanometers. The three different behaviours of the solid solutions below the solidus suggest that NaNO3–KNO3 might well be regarded as a system with limited solid solutions instead of a continuous series of solid solutions. The limited solid solution model seems to be more consistent with the phase diagrams obtained by differential scanning calorimetry. Copyright © 1999 John Wiley & Sons, Ltd.

207Pb NMR of Solid Solutions of Divalent Metal Nitrates.

207Pb NMR spectra of mixed crystals of anhydrous lead and strontium nitrate show up to 13 lines, arising from lead ions with 0-12 Pb(2+) nearest-neighbor cations replaced by Sr(2+). The shifted lines are further split by the multiplicity of inequivalent nearest-neighbor replacements. The average shift per Sr(2+) ion is 21.8 ppm. Similar but somewhat smaller effects are seen in [Pb,Ba](NO(3))(2) mixed crystals. The intensities of the resonances can be fit to Monte Carlo models of Pb(2+) and Sr(2+) ion distributions and are consistent with like nearest-neighbor pairs being 120 J/mol lower in energy than unlike pairs.

207PB NMR and Monte Carlo Studies of Ionic Solid Solutions

AbstractLead, strontium and barium nitrates, like the titanates of the same cations, form a continuous set of solid solutions. 207Pb NMR spectra of mixed crystals of lead/strontium nitrate and lead/barium nitrate each show up to 13 lines, arising from lead ions with from zero to twelve Pb2+ nearest-neighbor cations replaced by Sr2+ or Ba2+. In the case of (Pb,Sr)(NO3)2 these shifted lines are further split by the multiplicity of inequivalent nearest-neighbor replacements. The average shift per Sr2+ ion is 21.8 ppm; that for Ba2+ is smaller. Using Monte Carlo/Metropolis calculations, the intensities of the resonances can be fit to statistical models of Pb2+ and Sr2+ ion distributions, and used to probe the microenergetics of solid solution formation. The data can be satisfactorily fit by distributions in which the cations are slightly clustered, with like pairs of nearest neighbors being favored by 120 J/mol over unlike pairs. Interestingly, this finding is inconsistent with the conventional interpretation of powder diffraction results for the mixed crystals, where the dependence of lattice parameter on composition shows a slight positive curvature, generally held to indicate a favorable interaction between unlike ions.

Geometry and Electronic Structure of CuCl(6)(4-) Polyhedra Doped into (3-Chloroanilinium)(8)[CdCl(6)]Cl(4)-An EPR and Structural Investigation.

The EPR single-crystal and powder spectra of mixed crystals of (3-chloroanilinium)(8)(Cd(1-x)Cu(x)Cl(6))Cl(4) are measured as a function of temperature and x and analyzed with respect to the geometry and bonding properties of the CuCl(6) polyhedra. These undergo strong distortions due to vibronic Jahn-Teller coupling, with the resulting tetragonal elongation being superimposed by a considerable orthorhombic symmetry component induced by a host site strain acting as a compression along the crystallographic a axis. This strain becomes apparent in the cadmium compound (x = 0), whose crystal structure is also reported [a = 8.701(2) Å, b = 13.975(2) Å, c = 14.173(2) Å, alpha = 81.62(1) degrees, beta = 72.92(1) degrees, gamma = 77.57(1) degrees, triclinic P&onemacr;, Z = 1]. A calculation of the ground state potential surface and its vibronic structure nicely reproduces the g values, Cu-Cl spacings, and ligand field data. At high copper concentrations (including x = 1), the CuCl(6) polyhedra are coupled elastically, with the long axes of neighboring polyhedra having perpendicular orientations. The elastic correlation presumably is not of the long-range antiferrodistortive type, however. Above about 55 K, the angular Jahn-Teller distortion component becomes dynamically averaged within the time scale of the EPR experiment, leading to local tetragonally compressed CuCl(6) octahedra.

Infrared reflectivity spectroscopic studies on potassium ammonium dihydrogen phosphate systems

Abstract The polarized infrared reflectivity spectra of mixed crystals of potassium and ammonium dihydrogen phosphates : K1–x (NH4)x H2PO4, have been investigated in the temperature range 250 - 7 K, beween 15 and 600 cm−1, for several ammonium concentrations 0 < x <1. Results evidence a structural glass formation in the intermediate concentration range, and a double-mode behaviour of the translational optical lattice mode polarized along the c axis for all studied mixed crystals (0 < x < 1).

Infrared spectra of the dihydrates of calcium selenate and yttrium phosphate - comparison with the spectrum of gypsum

The infrared spectra of protiated and deuterated CaSeO 4·2H 2O and YPO 4·2H 2O were compared with the spectrum of gypsum (CaSO 4·2H 2O) with which the two investigated compounds are almost certainly iso- structural. From the position of the bands in the OD stretching region of the spectra of partly deuterated compounds having low deuterium content, one may conclude that the strength of the hydrogen bonds which water molecules form with the anions increases in the order sulfate, selenate, phosphate. While studying the spectra of mixed crystals, particular attention was payed to the bands originating from the stretching vibrations of the tetrahedral anions.