Octagonal crystals of strontium barium niobate (SBN: 61)

Strontium barium niobate (SBN: 61) crystals, as grown by the Czochralski technique, are normally round in cross section and the circumference is ringed by 24 facets. We have grown SBN: 61 crystals with low axial temperature gradient conditions and have obtained crystals which are octagonal in cross section.     

Ferroelectric domain structure in SBN crystals (Its statics and dynamics)

The domain structure and its switching mechanism are studied on various cleaved facets of single crystals of SBN solid solutions.     

Electrical conduction in ferroelectric lead hydrogen phosphate single crystals

Single crystals of LHP (Lead Hydrogen Phosphate) have been grown using the controlled reaction between lead nitrate and orthophosphoric acid solution by diffusion process in silica gel medium. Transparent crystals upto 6 × 4 × 3 mm³ in size have been grown at room temperature. The d.c. electrical conductivity of both single crystals and pelletized samples of LHP have been studied in the temperature range from 313 to 968 K. It has been observed that: (i) the d.c. conductivity of the crystalline sample is greater than that of thepellet sample, (ii) three distinct electrical conductivity processes have been observed and are interpreted as extrinsic, intrinsic, phase changes, and (iii) the activation energy for the conduction in the crystalline sample is greater than that of the pellet sample. The magnetic susceptibility measurements reveal that the paramagnetic characteristic of these materials and the implications are discussed.     

Temperature dependence of lattice parameters of SBN single crystals in the vicinity of their structural phase transitions

Changes of lattice parameters of Sr_xBa_1‒xNb₂O₆ (0.35 < x < 0.72) solid solution single crystals were measured as a function of temperature. The X‐ray Bond’ method was used to carry out very precise measurements of the lattice parameters. Fine correlations between values of the lattice parameter and the Sr concentration in the solid solution of Sr_xBa_1‒xNb₂O₆ single crystals are found. A conventional analysis of lattice parameter data in terms of spontaneous strain and strain/order parameter coupling shows that a normal structural phase transition does occur. While the ferroelectric system (SBN26) displays a nearly tricritical behavior, β ≈ 0.20, the relaxor one (SBN61) complies with the two‐dimensional Ising‐model‐like criticality, β ≈ 0.17.     

Effect of Cu Ions on the Dipole Moments and Polarization of Strontium Barium Niobate Single Crystals

The crystal growth, the ferroelectric hysteresis loops, and the infrared reflectivity spectra of coppermodified strontium barium niobate (SBN) single crystals are reported. Compared with the undoped SBN crystals, the copper-modified crystals have stable hysteresis loops, the spontaneous polarization of which is about 0.30 C/m², but that of the undoped SBN crystals is only about 0.12 C/m². Their coercive field strength is all about 340 V/mm. The experimental results of the infrared spectra show that the infrared reflectivities vary as the orientations of the dipole moments owing to the copper-doping. The c-axis becomes the most stable orientation of the dipole moments, and the polarization will be locked and won't recede if the copper-modified crystals are polarized into monodomains.     

Electical,Magnetic, and Thermal Properties of Cadmium Hydrogen Phosphate Hydrate Crystals

The d.c. electrical conductivity of pelletized samples of cadmium hydrogen phosphate hydrate (CHP) crystals have been studied in the temperature range 50 °C to 250 °C. It has been observed that CHP crystals exhibit ionic conductivity at 140 °C and possess semiconducting property. At room temperature CHP has stable crystal structure. From thermal analysis it is concluded that CHP crystals possess water of crystallization and the material to be diamagnetic.     

Switching Behaviour of Pb5Ge3O11 Single Crystals

Single crystals of lead germanate have been grown by Czochralski method. Hysteresis and switching pulses could only be measured after treating the crystal samples at elevated temperature and electrical a.c. field. Hysteresis is strongly frequency dependent. We observed the motion of the domain walls in polarized light simultaneously. The hysteresis loop is distorted at elevated temperature because of electric conductivity of the crystals. Temperature dependence of electric conductivity has been measured.     

Growth and Characterization of Single Crystals of the Ternary Compound TlGaTe2

The electrical conductivity and the Hall effect for TlGaTe₂ crystals have been measured over a wide temperature range. The crystal used for our study was grown by the Bridgman technique and possessed p-type conductivity. The energy gap has been found to be 0.84 eV, whereas the ionization energy has the value 0.25 eV. The variation of the Hall mobility as well as the carrier concentration with temperature was investigated. The scattering mechanism of the carrier in the whole temperature range of investigation was checked.     

Thermal conductivity of FeS2 pyrite crystals in the temperature range 50–300 K

The thermal conductivity of two single-crystal samples of pyrite FeS₂ are investigated by the method of stationary longitudinal heat flux in the temperature range 50–300 K. The low electrical conductivity of the crystals with a small impurity content causes an identical value of experimental lattice thermal conductivity. The temperature dependence of the phonon mean free path is established.     

过去10年晶体研究透视

通过对1991～1999年间MSCI数据库中有关晶体论文的计量分析,研究了近10年来晶体学科的发展轨迹。总体来看,晶体学科发展迅速,论文总量逐年以千篇之数快速增长,其中激光晶体论文数增长很快。在我们调查的多种功能晶体中,KDP和含铅铌酸盐晶体(PMN和PZN)近年来增长速率明显高于其它晶体,作为研究热点必将持续下去。SBN论文在近2～3年中也保持较高的数量。由于固液界面温度梯度较小以及容易批量生产等优点,垂直布里奇曼生长技术近年来颇受晶体研究人员的重视。     

Electrical Conductivity and Thermal Dehydration Studies of Mixed Single Crystals of BaCu(C2O4)2 · 6 H2O,Ba1–xCuxC2O4 · 4 H2O and Ba1–2x(NH4)2xC2O4 · 4 H2O

The measurement of electrical conductivity for the investigation of the number of water molecules present in the mixed crystals of barium copper oxalate and barium ammonium oxalate lattice have been carried out in the temperature range 30 to 450 °C. The dehydration temperature and the number of water molecules removed out of the structure at a particular temperature is estimated from the sharp increase in conductivity at these points. The almost steep increase of conductivity is attributed to the increase in the number of mobile charge carriers H⁺ and OH^– ions generated from the escaping water molecules. The study of electrical conductivity in association with the thermal behaviour has been used to understand the mechanism of conduction.     

Electrical conductivity of Cs<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> crystals

The electrical conductivity of Cs₂CuCl₄ single crystals, synthesized by crystallization from aqueous solutions in the CsCl–CuCl₂–H₂O system, has been investigated. The temperature dependence of the electrical conductivity of crystals in a temperature range of 338–584 K exhibits no anomalies. The electrical transfer activation enthalpy is ΔH_σ = 0.72 ± 0.05 eV and the conductivity is σ = 3 × 10^–4 S/cm at 584 K. The most likely carriers in Cs₂CuCl₄ are Cs⁺ cations, which transfer electric charge according to the vacancy mechanism.     

Electric and Dielectric Evaluation of KDP

Single crystals of potassium dihydrogen phosphate, KH₂PO₄ (KDP), grown by isothermal evaporation at room temperature have been characterized by their measurement of electrical conductivity and dielectric behaviour. Implications in respect of practical utility of KDP crystals in devices have been given.     

Transport property measurements in tungsten sulphoselenide single crystals grown by a CVT technique

The transport properties of ternary mixed WS_xSe_2‐x single crystals have been studied by measuring the thermo power, electrical conductivities and Hall parameters in a small temperature range 303‐423 K. The electrical conductivity was highest for selenium rich WSe₂ and lowest for sulphur rich WS₂ crystals. All the crystals showed semiconducting behaviour from the temperature dependence of ‘ρ’, ‘R_H’ and ‘S’. The Hall coefficients showed that the samples are p‐type conducting. The temperature dependence of resistivity, Hall coefficients, carrier concentration showed that all of them are thermally activated. The values of activation energies, pre‐exponential factors and the scattering parameters have been determined. The dominant scattering mechanism for the charge carriers has been explained. The relation between the TEP and the concentration of charge carriers and electrical conductivity was studied. The effective masses of holes and the effective density of states have been determined. These parameters show an increase with increase in sulphur content. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Aspects of Take Temperature Dependence of Electrical Conductivity in Polymeric Materials

The temperature dependence of the electrical conductivity of a number of polymeric organic and inorganic materials is described by a function, G(E,T), that is the derivative of the Fermi function. The mathematical justification for the use of this function in place of the Fermi function is described. Use of the G(E,T) function in the appropriate conductivity equation allows one to reproduce the temperature dependence of electrical conductivity in materials as diverse as (SN) and germanium single crystals, The function is found to be applicable to experimental conductivity data that collectively span a range of about 20 orders of magnitude, and a total temperature range of approximately 1000 K for the materials cited. The G(E,T) function adequately simulates the commensurate-incommensurate transition that is observed in materials such as (TMTSF)₂PF₆ and TTF-TCNQ. The importance of lattice order and the degree of single crystal perfection on derived properties of the conductivity curve are discussed. The G(E,T) function is applicable to other electron transport properties. The temperature dependence of electrical capacitance of SrTiO₃ is cited as an example,     

On the preparation and electrical properties of thallium selenide monocrystals

Thallium Selenide single crystals were prepared by a special design using Bridgmantechnique constructed by the authors. An investigation was made on the influence of temperature on the electrical conductivity and Hall effect in two crystallographic directions. The anisotropic properties were checked, and the anisotropic factor was observed to increase with temperature decrease. The energy gap as well as the ionization energy was calculated. The conductivity throughout the entire temperature range was found to be of p-type. The Hall mobilities derived from these measurements at room temperature were of the order μH_⟂ = 42.66 cm²/vs and μH_∥ = 112.2 cm²/vs.     

Electrical properties of ZnO single crystals annealed in a zinc atmosphere

The electrical conductivity and the Hall coefficient of ZnO single crystals annealed in a zinc atmosphere after growth were measured in a temperature range from 77 K to 1000 K. The results are compared with those of ZnO crystals from the zinc rich phase boundary. A shallow level with an activation energy at about 15 meV dominates in both groups of samples. Its concentration was found to correlate directly with the degree of non-stoichiometry.     

Electrical Conductivity of Cancrinite-Type Na8 − 2xCa x [Al6Si6O24][CO3] · 2H2O (x ≤ 0.03) Crystals

Crystallography Reports - The electrical conductivity of crystals of artificial cancrinite Na8 ? 2xCa x [Al6Si6O24][CO3] · 2H2O (x ≤ 0.03) has been studied in the temperature range...     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Evolution of growth and enhancement in power factor of InSb bulk crystal

Indium antimonide crystals were synthesized from the respective component elements using the vertical Bridgman technique. The grown crystals were characterized by using X-ray analysis, EDX, electrical conductivity and thermoelectric power measurements. The calculated structural parameters for the prepared crystal have a good agreement with the standard values. Crystallite size (D) of the obtained InSb crystals was calculated to be 62.4 nm. The measurements reveal higher values for Seebeck coefficient, electrical conductivity and power factor than the published results for the same compound.