Single crystals of In2Te5

Single crystals of semiconducting compound In₂Te₅ were grown by chemical transport employing iodine as a transport agent. The crystals had a plate-like habit with the [100] direction perpendicular to the flat surface of the platelets. Nominal dimensions are 10 × 1 × 0.05 mm. In₂Te₅ has a monoclinic structure with dimensions of the base centered cell: $\text{a}\text{= 13.47}\text{A}\text{?}$, $\text{b}\text{= 16.51}\text{A}\text{?}$, $\text{c}\text{= 4.365}\text{A}\text{?}$, β = 92°5′. The space group is $\text{C}{}_{\mathrm{<mtext>2</mtext><mtext>c</mtext>}}$. Pycnometric density is 5.96 g/cm³. The single crystals were all p-type. The conductivity, thermoelectric power and hardness were about 10^?5Ω^?1cm^?1, 650 mkV/°C, and 30 kg/mm², respectively. The minimum energy gap is 1.26 eV.     

The dielectric constants of CaWO4, Nd/CaWO4 and Gd/CaWO4

The dielectric constants and loss for pure single crystals of calcium tungstate and for neodymium- and gadolinium-doped crystals have been measured from 1 to 40 MHz. At 20? C the values for pure calcium tungstate areε _a′ = 11.3±0.4,ε _c′ = 9.1±0.4, at 1 MHz. These agree closely with Brower and Fang's data and increase very slightly with frequency. Doping at levels of less than 1.0 at.% produced no measurable change inε _a′ orε _c′. The dielectric loss, tanδ, which was isotropic, was about 5×10^?3 for all specimens at 1 MHz; at higher frequencies, tan? increased and, in the neodymium-doped crystals, the high frequency loss was found to be concentration dependent.     

AC conductivity and dielectric properties of Sb2Te3 thin films

Sb₂Te₃ films of different thicknesses, in the thickness range 300-620 nm, were prepared by thermal evaporation. X-ray analysis showed that the as-deposited Sb₂Te₃ films are amorphous while the source powder and annealed films showed a polycrystalline nature. The AC conductivity and dielectric properties of Sb₂Te₃ films have been investigated in the frequency range 0.4-100 kHz and temperature range 303-373 K. The AC conductivity σ_AC(ω) was found to obey the power law ω^s where s?1 independent of film thickness. The temperature dependence of both AC conductivity and the exponent s can be reasonably well interpreted by the correlated barrier hopping (CBH) model. The experimental results of the dielectric constant ε₁ and the dielectric loss ε₂ are frequency and temperature dependent and thickness independent. The maximum barrier height W_M calculated from dielectric measurements according to the Guintini equation agrees with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The effect of annealing at different temperatures on the AC conductivity and dielectric properties was also investigated. Values of σ_AC, ε₁ and ε₂ were found to increase with annealing treatment due to the increase of the degree of ordering of the investigated films. The Cole-Cole plots for the as-deposited and annealed Sb₂Te₃ films have been used to determined the molecular relaxation time τ. The temperature dependence of τ indicates a thermally activated process.     

Ionic conductivity of Li4GeO4, Li2GeO3 and Li2Ge7O15

The ionic conductivity of polycrystalline samples of three lithium germanates: Li₄GeO₄, Li₂GeO₃, and Li₂Ge₇O₁₅, has been determined using a c techniques and complex plane analysis. Conductivities at 400°C are 8.7 × 10^?5, 1.5 × 10^?5, and $\text{1.4 × 10}{}^{\mathrm{?7}}\text{(Ω·}\text{cm}\text{)}{}^{\mathrm{?1}}$ respectively. The conductivity of Li₄GeO₄ rises appreciably in the range 700–750°C.     

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

ZrO₂ films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO₂, were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10⁶ and 2.0 × 10⁶ V cm^?1. Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0?6.0) × 10¹¹cm^?2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between ?0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V² dependence for negative bias and an I ∝ V^2.6 to I ∝ V^3.4 dependence for positive bias.     

Growth and physical properties of ZnGeAs2

Single-phase poly crystalline chalcopyrite-structure ZnGeAs₂ ingots with an average grain size of 70 μm have been grown using a modified vertical Bridgman apparatus. The melting point of the compound was determined by differential thermal analysis (DTA) to be 860°C and corrected X-ray diffraction (XRD) peak positions were obtained. The crystals were p type with a room-temperature carrier concentration of 1.1 × 10¹⁹ cm^?3 and a corresponding mobility of 15 cm²/V s. A possible chalcopyrite-to-sphalerite phase transition, reported previously to occur to 812°C, was not observed either by DTA or by XRD of quenched samples.     

CuTa2O6 - crystal growth and characterization

The compound CuTa₂O₆ has been prepared as crystals from a Cu/O melt and found to be tetragonal ($\text{a}\text{= 7.510}\text{A}\text{?}$, $\text{c}\text{= 7.526}\text{A}\text{?}$) rather than cubic as reported in the literature. The coefficient of thermal expansion between room temperature and 1000°C was found to be 8.0 × 10^?6°C^?1. Electrical resistivity measurements on a crystal showed semiconductor behavior between room temperature ($\text{? = 2 × 10}{}^3\text{Ω}\text{cm}$) and 140°K ($\text{? = 7 × 10}{}^6\text{Ω}\text{cm}$) with an activation energy of E_A = 0.2 eV. Magnetic measurements between 4.2°K and room temperature showed Curie-Weiss behavior with a change in μeff at 120°K. For T>120°K, μeff = 1.76μ_B and θ_p = 0°K while for T<120°K μeff = 1.91 μB and θ_p = ?15°K.     

Crystal growth and structure determination of silicon telluride Si2Te3

Large single crystals of Si₂Te₃, which is the only stable phase in the SiTe system, were successfully grown by the Bridgman technique and by sublimation. Si₂Te₃ crystallizes in the trigonal space group P3?1c with a = 7.430 $\text{A}\text{?}\text{, C}\text{= 13.482}\text{A}\text{?}$, and z = 4. Using 856 independent intensities the structure was refined to R = 0.070. As compared to the GaS layer structure, Si₃Te₃ contains Si₂ units with SiSi bond distances of about 2.3 Å. In Si₂Te₃, however, only $\text{1}\text{4}$ of the Si₂ units run parallel to the c-axis direction, the others exhibit more complex orientations. Each Si is tetrahedrally coordinated by 3 Te and 1 Si, having SiTe bond lengths of about 2.55 Å. Each Te is bonded to only 2 Si atoms with SiTeSi bond angles around 93°.     

Etude de la conduction ionique de verres a base de ZrF4

The electrical and dielectric properties of new ZrF₄ based glasses have been studied in the frequency and temperature ranges 5Hz-500kHz and 130–280°C. Transport number measurements following Tubant's method showed that the glasses investigated are F^? conductors. The conductivities and activation energies for conduction are about 10^?6(Ωcm)^?1 at 200°C and 18 kcal.mole^?1 respectively. Preliminary interpretation of the change of conductivity with composition is given.     

Chemical vapor deposition and characterization of HfO2 films from organo-hafnium compounds

HfO₂ films were deposited on silicon substrates by the oxygen-assisted decomposition of hafnium β-diketonates at temperatures in the range 400–550 °C. These films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties. It was found that the films were fine-grained (approximately 325 Å) nearly stoichiometric monoclinic HfO₂. The films showed high resistance to most aqueous acids and bases. The deposits had a refractive index of 2.1 and an optical energy gap of 5.68 eV. The dielectric constant at 1 MHz was 22–25, and the dielectric strenght of the HfO₂ films varied between 2 × 10⁶ and 4.5 × 10⁶ V cm^?1. C-V measurements at 1 MHz indicated the presence of effective surface states which varied between 1.0 × 10¹¹ and 6 × 10¹¹ cm^t?2 for films that were deposited at temperatures higher than 500 °C or that were annealed at above 750 °C if deposited at 400–450 °C. The V_FB values were between ?0.6 and 0 V. The annealed films or films grown above 500 °C showed good bias-temperature stability. When positive bias and elevated temperatures were applied, the original C-V curve moved towards higher positive field values (0.2-0.5 V). After applying negative bias at elevated temperatures the C-V curved moved back in the direction of the original C-V curve. Measurements of the dependence of the current I on the electric field showed a dependence of I ∝ V² over a wide range.     

Crystal growth and characterization of Pt0.97S2

Large, well-formed plates of Pt_0.97 S₂ were grown by chemical vapor transport. A combination of phosphorus and chlorine was used as the transport agent. The best crystals were grown when the charge zone was maintained at 800°C and the growth zone at 740°C. The crystals were found to be diamagnetic with a susceptibility of ?31(2) × 10^?6 emu/mole at 77°K and showed semiconducting behavior with a band gap of 0.20(2)eV. From Hall voltage measurements, the sign of the carriers was ascertained to be positive. Pt_0.97S₂ particles less than 63μ underwent thermal decomposition in air at 270(10)°C.     

Cs2Si2Te6, ein polypertelluridosilikat (IV)

The new compound Cs₂Si₂Te₆ crystallizes in the monoclinic system (space group: Cc, No. 9) with the lattice constants a = 828.5(4) pm, b = 1393.5(6) pm, c = 1340.4(6) pm, ß = 100.35(12)°.Fivefold Si₂Te₃-rings, each formed by two SiTe₄ tetrahedra, connected by common Te atoms and Te-Te groups, are linked by Te bridges to infinite strings.     

Zur kenntnis von Na2Cu4S3 und KCu3Te2

The crystal structures of the new compounds Na₂Cu₄S₃ and KCu₃Te₂ have been solved. Na₂Cu₄S₃ crystallizes in the K₂Ag₄S₃ structure (space group: C2/m, a = 1563(3) pm, b = 386(2) pm, c = 1033(2) pm, β = 107.6^o, N = 4), KCu₃Te₂ in the CsAg₃S₂ structure (space group: C2/m, a = 1645.3(9) pm, b = 429.4(4) pm, c = 866.1(6) pm, β = 111.86^o, N = 4).     

Epitaxial growth of MgAl2O4 spinel crystals by solid-state reaction of MgO crystal with molten Al metal

Single crystals of MgAl₂O₄ spinel have been prepared epitaxially by a solid-state reaction of MgO crystal with molten Al metal under vacuum of 10^?5≈10^?6 torr at 1000≈1100°C. The growth rate was estimated to be about 0.1≈0.2 mm/hour in this temperature range. The as-grown crystals were black and opaque with low crystallinity, which was improved by heating above 1350°C. Chemical analysis showed that the crystals were slightly contaminated with Mg metal which was easily oxidized above 900°C in air.     

Resistivity studies on Ga2Te3 and In2Te3 under high pressures

The resistivities of III–VI semiconductors Ga₂Te₃ and In₂Te₃ were found to decrease abruptly under hydrostatic pressures between 1 and 7 GPa. The transition was reversible for Ga₂Te₃ but irreversible in the case of In₂Te₃ due to decomposition. These results are compared with the behaviour of II–VI and III–V semiconductors and transition pressures correlated with lattice constants.     

The preparation and characterization of dense,highly conductive Na5GdSi4O12 nasicon (NGS)

Na₅GdSi₄O₁₂ has been prepared via conventional ball-milling technique and through spray-freezing/freeze-drying. The ball-milled materials were calcined at 700°C or 925°C and sintered at 1050°C/3.5h to 89% dense multiphase ceramics. Spray-frozen/freeze-dried powders were calcined at 530°C and sintered at 1050°C/25 min to 99 ± 1% theoretical density. The latter material was single-phase NGS nasicon with a 300°C resistivity of 3.8 Ω·cm, an activation energy for Na⁺-conduction of 4.4 kcal/mol, a flexural strength of 105 MPa, a duplex grain structure with average sizes 0.4 μm and 3 μm and a unique linear thermal expansion coefficient (25–540°C; α = 12.6 × 10^?6/°C±4%).     

LiGeTe2, das erste kettenhypotelluridogermanat

The new compound LiGeTe₂ crystallizes in the triclinic system (space group PI) with the lattice constants: a = 725.5(3) pm, b = 913.2(4) pm, c = 1134.0(4) pmα = 75.75(5)°, β = 77.11(5)°, γ = 70.77(5)°. Octahedral Ge₂Te₆ - units are connected by common edges in such a way, that sixmembered Ge₄Te₂ - and fivemembered Ge₃Te₂ - rings form infinite strings.     

Crystal growth and magnetic anisotropy of YTiO3

Single crystals of YTiO₃ were grown from the melt by the Czochralski technique from molybdenum crucibles under purified argon. YTiO₃ melts congruently at about 1965 ± 30°C. The largest crystals were a few mm on a side. Measurements of the magnetic moment of oriented single crystals at 4.2K reveal that the b- and c-axes are easy axes of magnetization while the a-axis is hard. The saturation magnetization in either of the easy directions is 0.84 ± .01 μ_B mole^?1.     

Effects of Si-ion implantation on crystallization behavior of Ge2Sb2Te5 film

Crystallization and thermal stability of Ge₂Sb₂Te₅ (GST), the benchmark working material in phase-change non-volatile memory, were modified via Si-ion implantation. Through 5 × 10¹⁵ Si-ions/cm² ion-implantation, crystallization temperature increases from 165 °C to 177 °C. Furthermore, the activation energy of crystallization increases from 2.9 eV in the pristine film to 3.3 eV and 4.0 eV in films implanted with the doses of 5 × 10¹⁵ and 5 × 10¹⁶ Si-ions/cm², respectively. Temperatures corresponding to a 10-year failure-time increase from 83 °C in the pristine film to 96 °C and 107 °C in films implanted with 5 × 10¹⁵ and 5 × 10¹⁶ Si-ions/cm², respectively. Thermal stability of Si-ion implanted GST thus improves significantly. It was also found that grain growth is inhibited with higher implantation doses. In the case of the 5 × 10¹⁶ ion/cm² dose, the second-phase transition from face-centered cubic to hexagonal closed-packed structure of the GST is completely inhibited. However, crystallization time increases slightly due to Si-ion implantation.     

Phase relations in the InBr3 - In2Te3 system and the crystal structure of InTeBr

The quasibinary system InBr₃-In₂Te₃ contains the intermediate phase InTeBr, which melts peritectically at 477 °C. Crystals of InTeBr suitable for crystal structure determination were grown by Bridgman technique. InTeBr: monoclinic, $\text{P}\text{2}{}_1\text{c}$; a = 7.350, b = 7.577, c = 8.343 Å B = 117.61 °; d_x = 5.2 g cm^?3; Z = 4. Intensities were measured on an automatic diffractometer, and the structure was refined with anisotropic temperature factors to R = 9.9 %. The structure consists of InTe₃Br tetrahedra which are connected to layers parallel to the b/c-plane; the layers are translationally equivalent along the a - axis direction. Within a layer the tetrahedra form dimeric units (Br atoms in trans-terminal positions) by sharing common Te vertices to give a $\text{2}\text{∞}$ framework. Te atoms are surrounded by three In atoms in a distorted trigonal pyramidal arrangement. A band gap of about 2.45 eV for InTeBr has been determined by optical transmission measurements.