Photoelectrical properties of layered GaS single crystals and related structures

The photoconductivity of pure and Cu-doped layered gallium monosulfide (GaS) single crystals, and of Ni-GaS(Cu)-In and GaS(Cu)-ZnO structures, is investigated. The activation energies of surface states were found as 0.10 eV, 0.40 eV and 17 meV, ∼400 meV for GaS and GaS(Cu), respectively. Cu acceptor levels are localized at 0.44 eV and 0.52 eV above the valence band of GaS. ZnO-GaS(Cu) heterojunctions show remarkable photosensitivity in the wavelength range of 250-700 nm.     

Study of dielectric properties of RbNO3 single crystals

Dielectric properties, dielectric constant (k), dielectric loss (tan δ) and a.c. conductivity (σ) in the solution-grown single crystals of RbNO₃ are presented from room temperature to about 200°C covering the frequency range 10² to 10⁵ Hz. A broad peak observed in tan δ-frequency data between 10³ and 10⁵Hz is thought to be due to impurity-vacancy dipoles. The sudden rise of three parameters near 160°C is attributed to the known phase transition from trigonal to CsCl structure.     

Preparation and properties of thick LaMnO3-based films

Thick (50 ±10 μm) La_1-xSr_xMnO₃ (x = 0.2, 0.4) and La_0.7Ca_0.3Mn0₃ films were prepared by screen printing, and their electrical properties were studied. The films were found to be close in magnetoresistance and resistivity to bulk materials     

Face shear piezoelectric properties of relaxor-PbTiO(3) single crystals

Poling relaxor-PbTiO(3) single crystals along pseudocubic [011] results in a macroscopic symmetry of mm2, enabling a large face shear d(36) in Zt±45° cut crystals. In order to allow the determination of electrical properties by the resonance method, square samples are required. Using Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1∕3)Nb(2∕3))O(3)-PbTiO(3) crystals, piezoelectric d(36) coefficients were determined to be in the range of 2000-2500 pC∕N, with electromechanical coupling factor k(36)～0.80-0.83. Mechanical quality factor Q～180 and ultralow frequency constant of ～500 Hz m were obtained. Together with the wide temperature usage range (up to ～110 °C) and high ac driving field stability (～5 kV∕cm), such face shear crystals have a promising potential for ultralow-frequency-transducer applications.     

Dielectric properties of LiF single crystals

The dielectric constant,, loss, tan, and a.C. Conductivity, , of high quality single crystals of LiF have been measured in the frequency range 10² to 10⁵ Hz and in the temperature range 30 to 400° C. of LiF at 30° C is 8.3 and is frequency independent; tan was below detection level (tan<0.0001). increases slowly with temperature up to about 150° C (frequency independent region) beyond which it rises rapidly, being frequency dependent with larger values at lower frequencies. A similar behaviour is exhibited by tan . The activation energy for conduction in the high temperature region is calculated to be 0.93 eV from log against 1/T graphs. Log () against 1/T plots (where is the difference between the dielectric constant at any temperature and the value at room temperature, 30° C) yields an activation energy value of 1.0 eV in the high temperature region. This activation energy is found to be independent of frequency. This agreement between the two activation energy values, one for the a.c. conductivity and the other for the increase with temperature. This suggests that the same charge carriers are responsible for the two processes in the high temperature region.     

Preparation and some physical properties of Bi2−xInxSe3 single crystals

Bi_2–xIn _x Se₃ (x=0.00 to 0.66) single crystals were prepared using a modified Bridgmann method. Their homogeneity was studied by determining the indium content and the variations of Seebeck coefficient in the directions perpendicular and parallel to the crystal axis. X-ray structure analysis revealed that the volume of the unit cell of Bi_2–x In_xSe₃ crystal lattice decreases with increasing value of x. Measurements of the electrical conductivity, Hall constant and Seebeck coefficient showed that incorporation of the indium atoms into the Bi₂Se₃ crystal lattice results in an increase of free electron concentration for low indium content, whereas the free electron concentration is suppressed in the range of the high indium content. This effect is explained qualitatively on the basis of our ideas on the nature of point defects in Bi_2–x In_xSe₃ crystals.     

Growth and properties of CuInS2 single crystals

CuInS₂ single crystals 14–16 mm in diameter and up to 40 mm in length were grown by the traveling solvent method. The crystals were found to ben-type, with a conductivity of 0.1–10 S/cm, carrier concentration of 10¹⁶–10¹⁷ cm⁻³, and carrier mobility of 150–220 cm²/(V s). The anisotropic thermal expansion of the crystals was measured.     

Growth and properties of strontium cobaltate single crystals

Single crystals of strontium cobaltate with oxygen-deficient composition have been prepared by the floating-zone method using a lamp image furnace. Chemical and X-ray analyses showed that the composition was SrCoO_2.70 with a doubled perovskite structure of cubic cells, a ₀=7.710±0.001 Å. The crystal was ferromagnetic and its Curie temperature was 150 K. The effective Bohr magneton per ion of Co⁴⁺ was 1.21, suggesting that Co⁴⁺ is almost in the low spin state.     

Growth and electrical properties of Zn3P2 single crystals and polycrystalline ingots

A method to grow tetragonal -Zn₃P₂ single crystals from commercially available powder is reported. Thermal and growth duration conditions to increase crystal quality are given. The applicability of the Klosse-Ullersma model is discussed in this case, and optimized reactor dimensions are given. To grow polycrystalline ingots in a standard two-zone furnace from synthesis of elements, we propose a method which allows one to obtain single compact polycrystals with as-grown resistivities comparable to the best values reported for Zn₃P₂. Finally the growth of Zn₃P₂ and silver-doped Zn₃P₂ in the proportions 0.01 to 0.1 at% Ag per atom of zinc are for the first time reported. Crystallographic and electrical properties are also studied.On leave from the Departamento de Electricidad y Magnetismo, Facultat de Fisiques, Valencia, Spain.     

The cryogenic properties of Al-Li single crystals

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Electrical properties of undoped single CoO crystals

Electrical conductivity and Seebeck coefficient measurements have been carried out on undoped single CoO crystals in the temperature range of 289 to 548 K. All samples were found to be p type semiconductors. The mobility of charge carriers has been determined and the results are explained on the basis of hopping mechanism.     

Crystallization and physical properties of SbTiTaO6 single crystals

Optimum physicochemical conditions for a hydrothermal crystallization of antimony titanium tantalate SbTiTaO₆ (STT) at 190–225°C in the SbTiTaO₆-H₂SO₄-HCl-H₂O₂-H₂O system with various concentrations of acids and hydrogen peroxide. The dielectric and pyroelectric properties of synthesized STT single crystals were studied.     

Microstructure and electrical properties of LaMnO3-CaCu3Ti4O12 composite ceramics

In this study, xLaMnO₃-(1???x)CaCu₃Ti₄O₁₂ (0?≤?x?≤?0.7) composite ceramics have been prepared by the conventional solid-state method. XRD results show that the composite ceramics are mainly composed of LaMnO₃ and CaCu₃Ti₄O₁₂ phases. Electrical property analysis shows that the resistivity ρ₂₅ gradually decreases from 2.17?×?10⁸ to 1.74?×?10⁵ Ω·cm with increasing LaMnO₃ content. The relationship between lnρ and 1000/T is not linear and changes around 350 °C. In the temperature range of 0–350 °C, the activation energy Ea_0–350 °C decreases gradually with the increase of the LaMnO₃ content. In the temperature range of 350–500 °C, the activation energy Ea_{350–500 °C} increases first and then decreases, which is related to the variation of oxygen vacancy. The compounding of LaMnO₃ gives rise to the decrease in B value, thus, providing the potential for the applications of wide temperature range thermistors. After annealing, the coefficient of aging (ΔR/R) of the composites decreases from 23.73 to 3.01%.

     

Growth and some properties of sodium-cadmium formate single crystals

The growth of sodium-cadmium formate NaCd(HCO₂)₃ single crystals by slow cooling method and their characterization by selective stching, X-ray diffraction and IR absorption spectral techniques are reported. The dislocation density in the crystals is found to be 5·10² ? 2·10³ cm^?2. The compound crystallizes in orthorhombic unit cell with space group Pcca and Z = 4. The influence of metal ion on carboxylate stretching frequencies of polycrystalline samples is investigated and the possible correlations between spectra and structure considered.