Growth of ZnGeP<Subscript>2</Subscript> crystals from melt

Some features of the growth of ZnGeP₂ single crystals by the Bridgman method have been considered. The ratio of the thermal-conductivity coefficients of the liquid and solid phases of ZnGeP₂ at the melting temperature was estimated to be 2.3. It is established that, in the case of ZnGeP₂ growth on a seed, the most favorable crystallographic directions are 〈100〉 and 〈001〉. It is shown that annealing and electron irradiation significantly decrease the optical absorption coefficient in the impurity absorption region.     

Intermediates and transport phenomena in two‐temperature synthesis of ZnGeP2

High quality semiconducting ternary compound ZnGeP₂ was synthesized by a modified two‐temperature technique using high purity elemental zinc, germanium and phosphorus as the starting materials. Transport phenomena of zinc and phosphorus vapors and the major reaction intermediates, taking place in ZnGeP₂ formation, were studied by interrupting the synthesis process using quenching technique as well as by adjusting the temperatures of cold and hot zones. The powder X‐ray diffraction analysis showed that the major reaction intermediates were ZnP₂, Zn₃P₂, and GeP, which proportions were changed at the different temperature stages. ZnP₂ was formed in the temperature gradient region and ZnGeP₂ was formed in the hot zone when the temperature of the hot zone was higher than 900 °C. The 520‐1040 °C temperature profile was chosen for the ZnGeP₂ synthesis and charge amount per run reached 200 g. The powder X‐ray diffraction pattern of the synthesized ZnGeP₂ compound was in agreement with the standard pattern of ZnGeP₂. These results demonstrated that the synthesized ZnGeP₂ compound was a single phase. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature-concentration fields of the crystallization of YbAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> from high-temperature melt solutions based on potassium trimolybdate

The phase relationships in the YbAl₃(BO₃)₄-K₂Mo₃O₁₀-B₂O₃-Yb₂O₃ multicomponent system are investigated in the temperature range 1150–1000°C within the stability region of the YbAl₃(BO₃)₄ compound. The region of single-phase crystallization of the YbAl₃(BO₃)₄ borate is revealed in the section corresponding to the composition containing 15 wt % YbAl₃(BO₃)₄. For the same composition, it is demonstrated that there exists a correlation between the temperatures of saturation of melt solutions with the YbAl₃(BO₃)₄ borate and the composition of the solvent, namely, the contents of B₂O₃, K₂Mo₃O₁₀, and Yb₂O₃ in the solvent. The temperature dependences of the solubility of the YbAl₃(BO₃)₄ compound at different contents are determined for melts of two compositions: melt I containing 55 mol % K₂Mo₃O₁₀ and 45 mol % B₂O₃ and melt II containing 55 mol % K₂Mo₃O₁₀, 40 mol % B₂O₃, and 5 mol % Yb₂O₃. The specific features of the crystallization of the YbAl₃(BO₃)₄ compound are analyzed and compared with those of the yttrium, neodymium, gadolinium, and erbium aluminum borates studied previously.     

A new optical medium—Cd<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>F<Subscript>2</Subscript> single crystals

For the first time, single crystals of the Cd_0.75Sr_0.25F₂ solid solution with the fluorite structure are grown from melt by the Bridgman-Stockbarger method. The composition of these single crystals corresponds to the composition congruently melting at the minimum point on the phase diagram. The maximum diameter of the crystal is 50 mm; the maximum height is 30 mm. The vickers microhardness of the semitransparent crystals equals 191 ± 43 kg/mm². The transmission cutoff in the IR range is ～10 μm.     

Crystal structure of a new synthetic Ca,Li pentaborate: CaLi<Subscript>4</Subscript>[B<Subscript>5</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>2</Subscript>]<Subscript>2</Subscript>

When studying the phase formation in the CaO-Li₂O-B₂O₃-H₂O system, a new Ca,Li pentaborate was synthesized under hydrothermal conditions. The structure of a new compound with the crystallochemical formula CaLi₄[B₅O₈(OH)₂]₂ (sp. gr. Pb2n, a = 8.807(7), b = 9.372(7), c = 8.265(6) Å, V = 682.2(9) ų, Z = 2, d_calcd = 2.43 g/cm³, automated SYNTEX-\(P\bar 1\) diffractometer, 2690 reflections, 2θ/θ scan, λMo) is refined up to R_hkl = 0.0557 in the anisotropic approximation of atomic thermal vibrations with allowance for the localized H atoms. The structure of the Ca,Li pentaborate is formed by (010) open boron—oxygen layers formed by two independent [B₅O₈(OH)₂]^3? pentagroups, with each of them being formed by three B tetrahedra and two B triangles. The structure framework consists of the above boron—oxygen layers bound by isolated Li tetrahedra. The Ca cations are localized in the centers of eight-vertex polyhedra located in the [001] channels of the Li,B,O framework. Comparative crystallochemical analysis of the new Ca,Li pentaborate and Li pentaborate of the composition Li₃[B₅O₈(OH)₂]-II showed that the anionic matrices of both compounds are completely identical, whereas some of the cationic positions are different.     

Structural state of a radiation-modified Ti<Subscript>50</Subscript>Ni<Subscript>47</Subscript>Fe<Subscript>3</Subscript> single crystal

The structural state of a Ti₅₀Ni₄₇Fe₃ single crystal irradiated by fast neutrons (F = 2.5 × 10²⁰ cm⁻²) at 340 K was studied by thermal neutron diffraction at 78 and 295 K. The melt of this composition was chosen with the purpose of designing a radiation-resistant material exhibiting a shape-memory effect. It was found that the melt remains crystalline after irradiation, whereas the Ti₄₉Ni₅₁ crystal studied earlier becomes amorphous after an analogous irradiation. In spite of the fact that the main structural motif of the crystal remains unchanged after irradiation, martensitic transformations in the crystal do not occur and, consequently, the shape-memory effect is not retained. The radiation resistance of this class of crystals was estimated.     

Synthesis and crystal structure of the [Co<Subscript>2</Subscript>(Nicotinamide)<Subscript>4</Subscript>(C<Subscript>4</Subscript>H<Subscript>9</Subscript>COO)<Subscript>4</Subscript>(H<Subscript>2</Subscript>O)] complex

The [Co₂ L ₄(C₄H₉COO)₄(H₂O)] coordination compound of cobalt(II) valerate with nicotinamide (L) is synthesized and studied by IR spectroscopy. The crystal structure of the synthesized compound is determined. The crystals are triclinic, and the unit cell parameters are as follows: a = 10.2759(10) Å, b = 16.3858(10) Å, c = 16.4262(10) Å, α = 100.538(10)°, β = 101.199(10)°, γ = 90.813 (10)°, Z = 2, and space group P \(\bar 1\). The structural units of the crystal are dimeric molecular complexes in which pairs of cobalt atoms are linked by triple bridges formed by oxygen atoms of two bidentately coordinated valerate anions and a water molecule. The octahedral coordination of each cobalt atom is complemented by the pyridine nitrogen atoms of two nicotinamide ligands and the oxygen atom of the monodentate valerate group. The hydrocarbon chains of the valerate anions are disordered over two or three positions each.     

Synthesis and crystal chemical characteristics of the structure of <Emphasis Type="Italic">M</Emphasis><Subscript>0.5</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphates

Double phosphates of zirconium and metals with an oxidation degree of +2 of the composition M_0.5Zr₂(PO₄)₃ (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Sr, Cd, and Ba) are synthesized and characterized by X-ray diffraction methods and IR spectroscopy. The crystal structures of all the compounds are based on three-dimensional frameworks of corner-sharing PO₄-tetrahedra and ZrO₆-octahedra. Phosphates with large Cd²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ cations octahedrally coordinated with oxygen atoms form rhombohedral structures (space group R3), whereas phosphates with small tetrahedrally coordinated Mg²⁺, Ni²⁺, Cu²⁺, Co²⁺, Zn ²⁺, and Mn²⁺-cations are monoclinic (space group P2₁/n). The effect of various structure-forming factors on the M_0.5Zr₂(PO₄)₃ compounds with a common structural motif but different symmetries are discussed.     

Structural features of the KH<Subscript>2</Subscript>PO<Subscript>4</Subscript>: Cr single crystal

The precision X-ray structural investigation of KH₂PO₄ (KDP) crystal samples from different growth sectors of a single crystal containing chromium impurities is performed. It is demonstrated that the structure of the sample from the prismatic growth sector is more perfect than the structure of the sample from the pyramidal growth sector. The impurity trapping can lead to the formation of at least four different types of structural defects on the face of the pyramid, whereas only two of them can be formed on the face of the prism. A comparison with the relevant data for the “pure” KDP crystal shows that the number of defects and their character are approximately identical for all samples. The analysis of the IR spectra indicates that nitrate ions are contained in the samples from both growth sectors. Moreover, structurally bound water molecules and OH groups are revealed in the sample from the prismatic sector.     

Oxygen-conducting crystals of La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>: Growth and main properties

Single crystals of the anionic conductor La₂Mo₂O₉ are grown by crystallization from a nonstoichiometric melt. Their polymorphism and domain structure, as well as the temperature dependences of conductivity and dielectric permittivity, are studied. In the temperature range 750–600°C, the conductivity of these crystals is as high as 10^?1–10^?2 Ω^?1 cm^?1.     

Crystal structure of Ga<Subscript>0.5</Subscript>In<Subscript>1.5</Subscript>Se<Subscript>3</Subscript> solid solution

A solid solution of the GaIn₃Se₆ (2Ga_0.5In_1.5Se₃) composition with a hexagonal lattice (a = 7.051(3) Å, c = 19.148(2) Å, sp. gr. P6₁, z = 6, V = 824.4332(4) ų, ρ = 5.379(2) g/cm³) has been synthesized as a result of alloying Ga, In, and Se elements with a metal ratio of 1: 3. It was established that six out of nine In atoms in the lattice are located in a trigonal bipyramid, while the other three In atoms and three Ga atoms have a tetrahedral coordination.     

Structural study of new compound Bi<Subscript>2.53</Subscript>Li<Subscript>0.29</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> by the powder neutron diffraction method

A new compound of composition Bi_2.53Li_0.29Nb₂O₉ was synthesized in the course of the search for new materials with high ionic conductivity. Its crystal structure was determined from the neutron diffraction data. The new compound Bi_2.53Li_0.29Nb₂O₉ is crystallized in the orthorhombic system, sp. gr. Cmc2₁, and unit-cell parameters a = 24.849(1) Å, b = 5.4536(3) Å, and c = 5.4619(2) Å at T = 290 K (a = 24.843(2) Å, b = 5.4456(5) Å, and c = 5.4546(5) Å at T = 10 K). Within the temperature range 10–870 K, no structural phase transitions were revealed. The atomic coordinates and the thermal factors in the isotropic approximation were refined by the Rietveld method at 290 and 10 K. The data obtained were analyzed based on the calculated local balance of bond strengths.     

Structure and properties of antimony-doped lanthanum molybdate La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>

Polycrystalline samples of the composition La₂Mo_{2 − x} Sb _x O_{9 − y} , where 0 ≤ x ≤ 0.05, were prepared by solid-phase synthesis. Single crystals of La₂Mo_1.96Sb_0.04O_8.17 were obtained by spontaneous crystallization from flux. The structure of the metastable β _ms phase of this compound was determined at room temperature by X-ray diffraction. It was found that the La, Mo, and O1 atoms are displaced from the threefold axis on which they are located in the high-temperature β phase. It was shown that molybdenum atoms in the crystal structure are partially replaced by antimony atoms, which are located on the threefold axis. In antimony-doped crystals, lanthanum atoms partially return to the site on the threefold axis and the coordination environment of molybdenum cations becomes more ordered, thus facilitating the stabilization of the cubic phase at room temperature. Calorimetric measurements (DSC) showed that the introduction of Sb as the dopant into the La₂Mo₂O₉ structure leads to a decrease in the temperature of the α → β phase transition from 570 to 520°C and to the partial suppression of this transition. The temperature behavior of the conductivity confirms the DSC data. Thus, doping with Sb contributes to the stabilization of the cubic phase at room temperature.     

Novel Polyoxovanadate K<Subscript>2</Subscript>ZnV<Subscript>5</Subscript>O<Subscript>14</Subscript>: Crystal Structure and Peculiarities of Crystal Chemistry

A novel structure type has been established as a result of studying a non-merohedral microtwin of polyoxovanadate (K₂ZnV₅O₁₄) by X-ray diffractometry (R = 0.0595). The new compound, synthesized under hydrothermal conditions in the ZnCl₂–K₂CO₃–V₂O₅–H₂O system, is characterized as follows: a = 8.066(5) Å, b = 8.117(5) Å, c = 9.236(5) Å, β = 105.287(5)°, sp. P2₁/m, Z = 2, ρ_calcd = 3.54 g/cm³. Edge-shared five-core “clusters” consisting of vanadium octahedra, between which ZnO₄ tetrahedra (sharing vertices with octahedra) are located, form two-dimensional two-layer anion packets of the (ZnV₅O₁₄)^2– composition, alternating along the c axis with layers of potassium atoms. Structural peculiarities determine the morphology and color of new-phase crystals.     

Lead (II) selenite halides Pb<Subscript>3</Subscript>(SeO<Subscript>3</Subscript>)<Subscript>2</Subscript><Emphasis Type="Italic">X</Emphasis><Subscript>2</Subscript> (<Emphasis Type="Italic">X</Emphasis> = Br,I): Synthesis and crystal structure

Two lead selenite halides, Pb₃(SeO₃)₂Br₂ and Pb₃(SeO₃)₂I₂, have been prepared by solid-phase synthesis and structurally characterized. These compounds are isotypic and can be considered 3D with a microporous framework composed of lead polyhedra (distorted Archimedean antiprisms formed by oxygen and halogen atoms). The framework contains channels oriented in the [010] direction. These channels contain selenium atoms, which are bound with framework oxygen atoms belonging to different lead polyhedra.     

Ti/Zr isomorphism in wadeite: The crystal structure of the titanium-dominant K<Subscript>2</Subscript>(Ti<Subscript>0.55</Subscript>Zr<Subscript>0.45</Subscript>)Si<Subscript>3</Subscript>O<Subscript>9</Subscript> member of the series

The crystal structure of the titanium-rich mineral wadeite K₂(Ti_0.55Zr_0.45)Si₃O₉ from rischorrites of the Khibiny Alkaline Massif (Kola Peninsula, Russia) is studied by X-ray diffraction (XCalibur-S diffractometer, R = 0.0459): a = 6.8611(6) Å and c = 10.0611(9) Å; space group P6₃/m, Z = 6, D _x = 3.03 g/cm³. It is shown that the unit-cell parameters and volume of the mineral of mixed (Ti/Zr) composition are naturally intermediate between those of the terminal members of the isomorphous wadeite-based K₂ZrSi₃O₉–K₂(Ti_0.55Zr_0.45)Si₃O₉–K₂TiSi₃O₉ series. The expected correlation is due to the ionic radii of Zr⁴⁺ and Ti⁴⁺ which determine the lengths of Zr/Ti–O bonds in octahedra. The data of field observations and microscopic studies show that the Ti-dominant wadeite is formed on the basis of primary zirconium mineral in the course of a late imposed process under unique geochemical conditions.     

Controlled lattice constant mismatch by compositional changes in liquid phase epitaxially grown single crystal films of rare earth yttrium iron gallium garnets on gadolinium gallium garnet substrates

Liquid phase epitaxy (LPE) by dipping substrates into supercooled fluxed solution provides a convenient way of changing the melt and film composition. The apparatus, method and composition of the melts that we use will be described in detail. The composition of the layer is essentially Y₃GaFe₄O₁₂, which has a smaller lattice constant than the Czochralski-grown gadolinium gallium garnet substrate. By substitutions such as gadolinium, samarium or lanthanum for yttrium the lattice constant mismatch can be controlled. The effect of these substitutions on film properties such as cracks, stresses and magnetic domain pattern as well as the interaction of substrate defects such as dislocations with the epitaxially-grown film are discussed.     

Ionic conductivity of ScF<Subscript>3</Subscript> single crystals (ReO<Subscript>3</Subscript> type)

Electrical conductivity σ of ScF₃ single crystals (sp. gr. \(Pm\overline 3 m\), ReO₃ structure type) has been studied by impedance spectroscopy and compared with the electrical conductivity of rare earth HoF₃ (β-YF₃ type) and LaF₃ (tysonite type) trifluorides. ScF₃ crystals obtained by Bridgman directional solidification have ionic conductivity σ = 4 × 10^–8 S/cm at 673 K. It is smaller than the σ values for LaF₃ (sp. gr. \(P\overline 3 c1\)) and HoF₃ (sp. gr. Pnma) single crystals by a factor of 10⁴–10⁵. The low conductivity of ScF₃ crystals is due to the weak coordinating ability (coordination number CN = 6) and low electronic polarizability (α_cat = 1.1 ų) of Sc³⁺ ions. Mobile V_F⁺ vacancies and less mobile interstitial V_i^- ions (defects are formed according to the Frenkel mechanism) are involved in the ion transport. HoF₃ and LaF₃ single crystals have a high coordinating ability (CN = 9 for Ho³⁺ and CN = 11 for La³⁺) and a high electronic polarizability of cations (α_cat = 1.6–1.9 ų for Ho³⁺ and α_cat = 2.2 ų for La³⁺). Only mobile V_F⁺ vacancies (defects are formed according to the Schottky mechanism) are involved in ion transport.     

Low-temperature X-ray diffraction studies of [(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>NH<Subscript>2</Subscript>]<Subscript>5</Subscript>Cd<Subscript>3</Subscript>Cl<Subscript>11</Subscript> crystals

[(CH₃)₂NH₂]₅Cd₃Cl₁₁ crystals are grown by the method of isothermal evaporation from saturated aqueous solutions containing dimethylamine and cadmium chlorides, [(CH₃)2NH₂]Cl and CdCl_2.5H₂O. The crystal grown are studied by the X-ray diffraction method. It is established that the crystals are orthorhombic with the unit-cell parameters at room temperature a = 18.115 ± 0.004 Å, b = 11.432 ± 0.002 Å, and c = 15.821 ± 0.003 Å. The unit-cell parameters a, b, and c of the [(CH₃)₂NH₂]₅Cd₃Cl₁₁ crystals are measured as functions of temperature in the temperature range 100–320 K. The data obtained were used to determine the thermal expansion coefficients along the main crystallographic axes. The temperature curves of the unit-cell parameters and thermal expansion coefficients showed pronounced anomalies in the vicinity of the temperatures T ₁ = 120, T ₂ = 150, and T ₃ = 180 K corresponding to the phase transitions in the [(CH₃)₂NH₂]₅Cd₃Cl₁₁ crystals. The crystals are also characterized by a pronounced anisotropy of thermal expansion.     

Growth and structure of La<Subscript>3</Subscript>Zr<Subscript>0.5</Subscript>Ga<Subscript>5</Subscript>Si<Subscript>0.5</Subscript>O<Subscript>14</Subscript> crystals

The complete X-ray structure determination of Czochralski grown La₃Zr_0.5Ga₅Si_0.5O₁₄ single crystals with the Ca₃Ga₂Ge₄O₁₄ structure is performed (sp. gr. P321, a = 8.226(1) Å, c = 5.1374(6) Å, Z = 1, Mo K_α1 radiation, 1920 crystallographically independent reflections, R = 0.0166, R_w = 0.0192). The absolute structure is determined. It is shown that possible transition of some of La atoms (～1.2%) from the 3e to 6g position may give rise to the formation of structural defects.