X-ray studies of thermal expansion and phase transitions in (NH4)2SbF5 crystals

X-ray diffraction studies of phase transitions in (NH₄)₂SbF₃ single crystals have been made by using the Bond-type diffractometer for high-precision measurements of the unit-cell dimensions in a function of temperature. The principal linear thermal expansion coefficients and the linear Eulerian strain tensor have been calculated in the temperature interval 110 – 298 K. The phase transition diagram was proposed and the sequence of the phases has been compared with the results of other experimental techniques (NMR, NQR, DTA, electrophysical methods).     

Growth and properties of Nb-or Sn-doped KTiOPO4 crystals

Single crystals of potassium titanyl phosphate, KTiOPO₄, doped with Nb or Sn to various doping levels are grown by crystallization from flux. Their atomic structure and physical properties are studied. It is found that both dopants greatly affect the configuration of titanium-oxygen polyhedra and, hence, the ferroelectric and nonlinear optical properties of the crystals. Superionic transitions with abrupt changes in electrical conductivity are observed in some crystals for the first time.     

Dependence of photochromic damage on polarization in KTiOPO4 crystals

Studies of photochromic damage induced in KTiOPO₄ single crystals by 514.5 nm laser irradiation is reported. A dependence of photochromic damage on polarization was observed. Along the same propagation direction (θ=90°, ϕ=23.3°), the gray-track susceptibility for ∥z polarization irradiation is one order magnitude lower than that for ⊥z polarization irradiation for KTP crystal. The results clearly show that in KTiOPO₄, a correlation exists between the gray-track susceptibility and the ionic electrical conductivity. Due to a high ionic electrical conductivity along the polar z-axis, the optical absorption centers will be annihilated with ∥z polarization irradiation as soon as they are produced. This results in a lower gray-track susceptibility for ∥z polarization irradiation.     

Growth, structure, and properties of KTiOPO4 crystals doped with iron

A series of iron-doped KTiOPO₄ (KTP: Fe) single crystals in which iron substitutes for 0.1–0.3% titanium was grown. The structure of the KTP: Fe crystals was determined, and their dielectric and conducting properties were studied. An X-ray diffraction analysis failed to reveal such asmall amount of Fe⁺³ ions in titanium octahedral positions of the structure. It was found that an increase in the iron concentration results in a lowering of the symmetry of Ti(1)O₆ and Ti(2)O₆ octahedra. The splitting of the dielectric anomaly due to the ferroelectric phase transition was explained by the mechanism of incorporation of an impurity into different growth pyramids of the crystals. It was established that the aging of the KTP: Fe crystals leads to changes in the permittivity and electrical conductivity during long storage.     

New model of the bond diffractometer for precise determination of lattice parameters and thermal expansion of single crystals

A new model of diffractometer for very precise measurements (1 ppm accuracy) of lattice parameters and thermal expansion is presented. Special attention is paid to the temperature control and stability in a wide range from liquid nitrogen up to 800 K. Two examples of the application of the diffractometer in a study of solid state phase transitions are given.     

X-ray and Raman studies of single crystals of CsSbF6

Crystals of CsSbF₆ belong to the rhombohedral space groupR¯3-C _3i ² witha=7.904(1)andc=8.261(1) Å,V=446.95 ų,Z=3,D _c=4.11 gcm^–3. The antimony atom is surrounded by six fluorine atoms in a nearly perfect octahedral configuration with Sb-F 1.875(9) Å, while 12 fluorine atoms surround the cesium atom with closest contact 3.116 Å. Polarized Raman spectra of single crystals of CsSbF₆ have been obtained, and it is shown that these results can be interpreted in terms of a unimolecular rhombohedral structure. The small distortion from an octahedral arrangement for the SbF ₆ ^– group is clearly reflected in the spectra. The Raman results are in better agreement with the space groupR¯3m-D _3d ⁵ than withR¯3-C _3i ² , but this conclusion must be regarded with caution since the two features in the vibrational spectra of CsSbF₆ which can be used to distinguish between the two structures are weak and ill-defined.     

Growth,spectral and thermal studies of ibuprofen crystals

RS ‐Ibuprofen was crystallized for the first time in silica gel under suitable pH conditions by reduction of solubility method. The grown crystals were characterized by single crystal X‐ray diffraction and density measurement. The functional groups present in the crystal were identified using Fourier transform infrared spectroscopy. Optical bandgap energy of ibuprofen was estimated as 3.19(3) eV from UV‐Vis spectrum. Thermogravimetric analysis revealed that ibuprofen is thermally stable upto 102.9 °C and the initial loss of mass was due to evaporation only. Morphological study showed that the growth is prominent along b‐axis and the prominent face is {100}. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of rhodium incorporation in KTiOPO4 single crystals grown from self‐flux

The presence of an impurity like rhodium in the platinum crucible used for the growth of KTiOPO₄ (KTP) single crystals can have severe consequences in the performance of devices made from these crystals. In the present study the effect of rhodium incorporation has been investigated. Rhodium‐incorporated KTP crystals have a lower ionic conductivity (1.3 × 10^–7 S/cm at 100 kHz) than pure KTP crystals (3.5 × 10^–6 S/cm at 100 kHz) along the c‐axis. And the optical absorption in the green‐wavelength regime leads to a detrimental effect on their SHG performance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology of {100} and {201} faces and the optical quality of KTiOPO4 crystals

Crystallography Reports - Potassium titanyl phosphate crystals up to 350 g in weight have been grown from a high-temperature solution in K4P2O7 by the flux method on a [100]-oriented seed. The...     

水热法掺铌KTiOPO4晶体的形貌和缺陷研究

采用水热法在双温区加热炉中以Z-切向晶片为籽晶生长了掺铌KTiOPO4单晶(Nb∶KTP),得到尺寸为24.7mm×14.7 mm×42.6 mm的透明晶体。研究了Nb∶KTP水热条件下的生长习性和宏观、微观缺陷,通过其与纯KTP的透过谱的对比,对晶体质量进行了初步评估,与高质量的水热高抗灰迹KTP晶体有相当的质量。     

Spectroscopic, thermal and structural studies on manganous malate crystals

Prismatic crystals of manganous malate have been prepared by controlled ionic diffusion in hydrosilica gel. The structure was elucidated using single crystal X-ray diffraction. The crystals are orthorhombic with space group Pbca. Vibrations of the functional groups were identified by the FTIR spectrum. Thermogravimetric and differential thermal analyses (TG-DTA) were carried out to explore the thermal decomposition pattern of the material. Structural information derived from FTIR and TG-DTA studies is in conformity with the single crystal XRD data.     

Low-temperature dehydration of gypsum single crystals

On the basis of the analysis of the electron spin resonance spectrum of the SO ₃ ^? radical ion, it is established that the transformation of gypsum (CaSO₄ · 2H₂O) into bassanite (CaSO₄ · 0.5H₂O) with partial removal of water molecules occurs through the formation of an anhydrous metastable phase. This phenomenon, reflecting the processes of recrystallization of materials of this class, serves as the scientific basis for the production of binders from sulfate mineral associations.     

X-ray determination of thermal expansion of Na(ClO3)x(BrO3)1−x mixed crystals

Lattice constants of sodium chlorate and sodium bromate and their mixed crystals were determined over the temperature range from room temperature to 320 °C. The observed lattice constants for the various compositions show strong deviations from those expected from Vegard's rule. The lattice constants at various temperatures were fitted to polynomials of type a = a₀ + a₁t + a₂t². The linear coefficients of expansion for the Na(ClO₃)_x · (BrO₃)_1−x series varies non-linearly with composition showing negative deviations from linearity.     

X-ray topographic studies of the melting of nearly perfect gallium crystals

The temperature dependence of the concentration and shape of long dislocation lines in pure, nearly perfect gallium crystals has been measured by X-ray topography in anomalous transmission (Borrmann-topography). The dislocation structure did not change appreciably between temperatures of 22°C and at least 0.1 mK below the melting point T_m = 29.75°C. A few dislocations decreased their length due to tempering at the melting point. Pre-melting effects could not be detected.     

Deformation and microhardness studies on KClO4 single crystals

The deformation characteristics of KClO₄ single crystals have been studied by the methods of static and dynamic indentation on (001) plane. The cracks produced by the dynamic indentation have been interpreted in terms of slip-twin interactions. Also, the load dependence of Vickers microhardness and its anisotropy in this crystal are reported. The observed hardness anisotropy has been used to confirm the indices of the slip system 〈101〉 〈111〉 operative in this crystal at ordinary temperatures.     

Determination of lattice parameters and thermal expansion of CuGe2P3 + 0.2 Ge3P4 at elevated temperatures

CuGe₂P₃ is a p‐type semiconductor with zincblende structure. Ge₃P₄ is soluble up to 35 mole% in CuGe₂P₃. Lattice parameters of CuGe₂P₃ + 0.2 Ge₃P₄ have been determined at elevated temperatures from room temperature to 873 K using the x‐ray diffraction profiles (111), (200), (220), (311), (222), (400), (331), (420), (422) and (511) obtained from high temperature diffractometer. It is found that the lattice parameter increases linearly from 0.53856 nm at RT to 0.54025 nm at 873 K. The data on lattice parameter is used and coefficient of lattice thermal expansion of CuGe₂P₃ +0.2 Ge₃P₄ was determined at different temperatures. It is found that the coefficient of thermal expansion of CuGe₂P₃ +0.2 Ge₃P₄ is 5.48 x 10^‐6 K^‐1 and is independent of temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase transition studies in certain thermotropic liquid crystals thermal microscopy and DSC

Investigations on the phase transition studies in the thermotropic liquid crystals, (1) pcyanophenyl trans-4-propylcyclohexane carboxylate, (2) p-cyanophenyl trans-4-pentyl-cyclohexane carboxylate, (3) 4′-n-pentyloxy-4-cyanobiphenyl and (4) 4′-n-octyloxy-4-cyanobiphenyl are carried out by the thermal microscopy and the differential scanning calorimetric (DSC) studies. These studies reveal that the first three mesogens exhibit a single mesophase while the fourth one exhibits a smectic A phase in addition to the nematic phase. The textures exhibited by these mesogens in their mesophases and their transition temperatures, enthalpies and entropies are presented.