Thermal expansion of corundum structure Rh2O3

The directional thermal expansion coefficients of the corundum structure form of Rh₂O₃ were determined from room temperature to 850°C by x-ray diffraction methods. Rh₂O₃ has a lower thermal expansion and is less anisotropic in thermal expansion than alumina. The directional thermal expansion coefficients of Rh₂O₃ expressed in second degree polynominal form are: $\text{“α}{}_{\mathrm{<mtext>a</mtext>}}\text{” = 5.350 ×10}{}^{\mathrm{?6}}\text{+ 1.281 ×10}{}^{\mathrm{?9}}\text{T}\text{? 1.133 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$ and $\text{“α}{}_{\mathrm{<mtext>c</mtext>}}\text{” = 5.246 ×10}{}^{\mathrm{?6}}\text{+ 6.369 ×10}{}^{\mathrm{?9}}\text{T}\text{? 7.480 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$.     

Crystal structure and magnetic properties of Cu4NiSi2S7

The structure of the compound Cu₄NiSi₂S₇ has been determined. It crystallizes in a new, monoclinic distorted sphalerite superlattice with the parameters: $\text{a}\text{= 11.551}\text{A}\text{?}$, $\text{b}\text{= 5.313}\text{A}\text{?}$, $\text{c}\text{= 8.165}\text{A}\text{?}$, β = 98.72°, $\text{V}\text{= 495.2}\text{A}\text{?}{}^3$, Z = 2, space group C2. The analogous compound Cu₄NiGe₂S₇ is isotypic. At a Neél temperature T_N = 20.2 K, Cu₄NiSi₂S₇ becomes antiferromagnetic. The magnetic moment of the paramagnetic phase is 2.6μ_B.     

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.     

Contribution a l'etude de la conductivite ionique de l'orthophosphate Na3PO4

The present work is concerned with the ionic conductivity of pure trisodium orthophosphate Na₃PO₄, devoid of any trace of hydroxide NaOH. At the allotropic transition (330°C), we observe a jump of the ionic conductivity and a slight decrease in the activation energy (ΔE = 0,70 ± 0,02 eV for the quadratic variety and ΔE = 0,60 ± 0,04 eV for cubic γ-Na₃PO₄). Na₃PO₄ can be considered to be an electrolytic solid with medium conductivity ($\text{σ = 1.10}{}^{\mathrm{?4}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 370°C).     

Growth,electrical and photoelectrical properties of Tl3SbS3single crystal

The growth of Tl₃SbS₃ single crystal is reported for the first time. 5×1×1 cm³ ingots are obtained by using vertical Bridgmann method with a 2°C/mm gradient and a 0.7 mm/h growth rate. Intrinsic conductivity and photoconductivity are investigated. The weak dark conductivity, $\text{～ 10}{}^{\mathrm{?10}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300° K, contrasts with a strong photosensitivity. The value of the fundamental band gap deduced from spectral dependence of the photocurrent is in rather good agreement with the value 1.61 eV obtained from temperature dependence of the dark conductivity. The Lux-Ampere characteristics can be described by I ∝ L ^α but changes in α with illumination intensity and temperature show that at least two different local centers are involved in the carrier recombination mechanism.     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.     

Electrical and optical properties of MoSe2 films prepared by r.f. magnetron sputtering

The electrical resistivity of MoSe₂ films prepared by r.f. magnetron sputtering was measured between 300 and 10 K. The main sputtering parameter governing the physical properties of the films was found to be the substrate temperature T_sub. The room temperature resistivity of the as-sputtered films increased from $\text{1.7 × 10}{}^{-1}\text{Ω}\text{cm}$(T_sub = -70 °C) to $\text{1.4 × 10}{}^1\text{Ω}\text{cm}\text{(T}{}_{\mathrm{<mtext>sub</mtext>}}\text{= 150 °}\text{C}\text{)}$. A check of the thermo-electrical response showed that the majority charge carriers are holes except for films deposited at T_sub = 150 °C which are n type. Hall effect measurements indicated very low Hall mobilities (3–5 cm² V^-1 s^-1). Thermal annealing increased the room temperature resistivities by more than one order of magnitude for the specimens sputtered at a low substrate temperature. The optical properties were weakly influenced by the process conditions. The optical gap was determined to be 1.06 eV.     

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.     

An outline of the crystal-structure of Bi2Mo2O9

An outline of the structure of the catalyser component Bi₂Mo₂O₉ has been determined from X-ray powder diffractometer diagrams. The space group is $\text{P}{}^2\text{l}\text{n}$ ($\text{=}\text{P}{}^2\text{l}\text{c}$) with cell constants: $\text{a}\text{= 11.946 (2)}\text{A}\text{?}$, $\text{b}\text{= 10.795 (2)}\text{A}\text{?}$, $\text{c}\text{= 11.876 (2)}\text{A}\text{?}$ and β = 90.15 (2)°. There are eight formula units per cell. The positions of the metal-ions could directly be derived from the intensities of the strongest reflexions. With difference terms calculated from 19 strong reflexions a Δ F-synthesis was calculated, which revealed the approximate positions of the O^2?-ions. From packing considerations it was apparent that of 9 0^2?-ions one is only coordinated by Bi³⁺ and that Mo⁶⁺ must be tetrahedrally surrounded by 0^2?. These tetrahedra may be strongly distorted. The structure is not related to the scheelite-structure as has been assumed by some authors.     

Syntheses and magnetic properties of Eu3B2O6 and Sr3B2O6

Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions $\text{a}{}_{\mathrm{R}}\text{=6.697}\text{A}\text{?}$, α_R=85.17° for Eu₃B₂O₆, and $\text{a}{}_{\mathrm{R}}\text{=6.695}\text{A}\text{?}$, α_R=85.00° for Sr₃B₂O₆. The equivalent hexagonal lattice parameters are $\text{a}{}_{\mathrm{H}}\text{=9.069}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.542}\text{A}\text{?}$, and $\text{a}{}_{\mathrm{H}}\text{=9.046}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.566}\text{A}\text{?}$ respectively. Eu₃B₂O₆ appears to be ferromagnetic below 7.5K.     

Characterization of antimony-doped tin oxide films for solar cell applications

Transparent conducting undoped tin oxide (SnO₂) and antimony-doped tin oxide (ATO) films were deposited onto Pyrex glass and single-crystal silicon substrates using an inexpensive chemical vapour deposition system. SnCl₂ and SbCl₃ were used as the source reagents with oxygen and nitrogen respectively as the carrier gases. The deposition conditions were as follows: temperature, 350–500 °C; oxygen flow rate, 0.8–3.25 1 min^-1; nitrogen flow rate, 0–0.1 1 min^-1; deposition time, 5–20 min. The antimony concentration in the film and its physical properties were the same on both substrates. A figure of merit (Tr¹⁰/R_sh where Tr is the transmission at a particular wavelength and R_sh is the sheet resistance) was used to compare the performance of these films. The maximum figure of merit for SnO₂ films $\text{(1.43 × 10}{}^{-3}\text{Ω}{}^{-1}\text{(}\text{Tr}\text{= 95\% and R}{}_{\mathrm{<mtext>sh</mtext>}}\text{= 420 Ω/□))}$ was obtained when they were deposited at 500 °C with oxygen at a flow rate of 1 1 min^-1. The sheet resistance of antimony-doped films is a minimum at 3 mol.% Sb and the transmission decreases as the antimony concentration increases. The maximum figure of merit obtained for ATO films was $\text{6.78 × 10}{}^{-3}\text{Ω}{}^{-1}\text{(}\text{Tr}\text{= 90.6\% and R}{}_{\mathrm{<mtext>sh</mtext>}}\text{= 55 Ω/□)}$ for an antimony content of 3 mol.% and a nitrogen flow rate of 0.07 1 min^-1. These results are explained theoretically and are compared with those reported by other workers.     

The formation process and the electrical nature of the lock-on filament in Ge0.09As0.20Te0.71 glass

Lock-on (memory) phenomena observed in the amorphous semiconductor Ge_0.09As_0.20Te_0.71 have been investigated. The threshold voltage, V_th, and sample resistance, R, were measured during the formation of the filament. A relationship was obtained between the parameters V_th and R during the formation process. The electrical conductivity of the lock-on filament was deduced to be $\text{≈ 1.1 × 10}{}^4\text{Ω}{}^{\mathrm{?1}}\text{m}{}^{\mathrm{?1}}$. The influence of an existing lock-on filament on the formation of a new filament is also described.     

Etude des proprietes structurales et electrioues d'un nouveau conducteur anionique: PbSnF4

Three allotropic varieties of PbSnF₄ - α, β and γ - have been detected by DTA and X-ray diffraction. The α ai β and β ai γ transitions are reversible and occur at 80 and 355°C respectively. The high temperature form γ - PbSnF₄ is cubic and of fluorite type. The structures of the tetragonal β - PbSnF₄ and the orthorhombic α - PbSnF₄ forms are derived from the same structural type. PbSnF₄ has a high anionic conductivity ($\text{σ200°C ? 10}{}^{\mathrm{?1}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$). The temperature dependence of the conductivity indicates the existence of a break in the activation energy at 90°C.     

Ionic conductivity in low carnegieite compositions based on NaAlSiO4

Carnegieite compositions of the type Na_1+xAl_1+xSi_1?xO₄ with x = 0 to ～0.7 were prepared. Na ion conductivities, measured with Na and Au electrodes at ～10³ Hz, range from $\text{4×10}{}_{\mathrm{?5}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ for NaAlSiO₄ to $\text{5×10}{}^{\mathrm{?3}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300 C for Na_1.7Al_1.7Si_0.3O₄. Substitutions of Li, K, Ca, or Sr for Na lowered σ whereas substitution of Ti for Si raised σ. Na aluminum silicates with the nepheline structure had lower σ than carnegieite compositions.     

Carburization and decarburization kinetics of iron in CH4 — H2 mixtures between 1000 – 1100 °C

In this study the rate constants of the methane decomposition reaction on iron surfaces were determined in the 1000–1100°C temperature range, by grav? metric methods. Earlier works showed that the reaction velocity was given by The results indicate that the constant values vary from 2.72 × 10^?6 to $\text{16.74 × 10}{}^{\mathrm{?6}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for k and 2.61 × 10^?8 to $\text{8.62 × 10}{}^{\mathrm{?8}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ for k′ between 1000 and 1100°C.     

Structure determination of (3D) P2NbS8

Tridimensional P₂NbS₈ crystallizes in P4?n2 tetragonal space group, with $\text{a}\text{= 12.0483(4)}\text{A}\text{?}$, $\text{c}\text{= 7.2070(5)}\text{A}\text{?}$, $\text{V}\text{= 1046.2(1)}\text{A}\text{?}{}^3$ and Z = 4. The structure was anisotropically refined down to R = 2.3% from 468 reflexions and 53 variables. It is built from [Nb₂S₁₂] biprismatic bicapped units (average $\text{d}{}_{\mathrm{Nb?S}}\text{= 2.571}\text{A}\text{?}$) made of S^?II and S^?II₂ anions (dianionic distance of 2.014(3) Å). The niobium atoms are found as isolated Nb^IV ? Nb^IV pairs ($\text{d}{}_{\mathrm{Nb?Nb}}\text{= 2.859(1)}\text{A}\text{?}$) in these niobium group otherwise linked to each other through (PS₄) tetrahedral units (average $\text{d}{}_{\mathrm{P?S}}\text{= 2.051}\text{A}\text{?}$) themselves constituting interbonded [P₄S₁₂] rings. The P₂NbS₈ three-dimensional network thus obtained is compared to the (2D) P₂NbS₈, layered phase already described.     

Conductivite electrique et spectres de diffusion raman des verres mixtes AgPO3 − MI2 AVEC M = Cd,Hg, Pb. Correlation entre conductivite et structure

The glass-forming regions in the AgPO₃ ? MI₂ systems with M = Cd,Pb,Hg were determined. Electrical conductivity measurements and Raman spectra were carried out. A maximum conductivity value of $\text{10}{}^{\mathrm{?2}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is obtained for a mole fraction of 0,19 in PbI₂ or in CdI₂, whereas a value of $\text{3×10}{}^{\mathrm{?5}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is found for a mole fraction of 0,5 in HgI₂. The conductivity results and Raman spectra are examined and compared with those of AgPO₃ ? AgI. An exchange between Ag⁺ and M²⁺ ions is proposed leading to AgI species in AgPO₃ ? CdI₂ and AgPO₃ ? PbI₂ glasses. It could explain the high conductivity values obtained and the similarities observed in Raman spectra.     

Polycrystalline hydronium ββ″alumina: A ceramic fast proton conductor

Polycrystalline hydronium $\text{β}\text{β″}\text{-}\text{alumina}$ with f(β) of 0.16 to 0.25 has been fabricated with an electrical conductivity of $\text{～ 10}{}^{\mathrm{?2}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 22°C and an activation energy of 0.24 eV (T < 100°C) and 0.09 eV (T > 100°C). This is comparable with single crystal behaviour. Proton magnetic resonance is correlated with conductivity and the effects of disorder on the conduction plane of the β″-alumina structure are shown to be important.     

Some experimental observations on the Poisson's ratio of sea-ice

Measurements were made on the longitudinal and transverse strain of sea-ice beams loaded in flexure. The specimens were tested with stress rates varying from 10 to 600 kPa s^?1 and temperatures ranging from ?5°C to ?40°C. Under these conditions, the effective strain ratio μ increases with increasing temperature and decreasing stress rate. The strong influence of the stress rate, σ, suggests an empirical law of the form: μ = 0.24$\text{(}\text{σ}\text{?}\text{σ}\text{?}{}_1\text{)}{}^{\mathrm{?0.29}}\text{+ μ}{}_{\mathrm{D}}$ where σ is the stress rate (kPa s^?1), $\text{σ}\text{?}{}_1$ is a unit stress ratio (1 kPa s^?1) and μ_D is a dynamic value of Poisson's rate which depends on the temperature.     

A series of rare earth silicates RE3+2M3+[SiO4]2 (OH)

A series of isotypic silicates of composition RE₂M[SiO₄]₂ (OH) with RE = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and M = Al³⁺, Fe³⁺ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La₂Al[SiO₄]₂ (OH) (La₂Fe[SiO₄]₂ (OH)) $\text{a}{}_{\mathrm{o}}\text{= 7.401 (7.346)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 5.702 (5.862)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 17.072 (97.196)}\text{A}\text{?}$, gb = 112.4 (112.5°), $\text{P}\text{2}{}_1\text{c}$, Z=4.