Oxidation-reduction reactions of CeMO4+x (M = Ta or Nb) phases

Phase equilibrium methods, single crystal and powder x-ray diffraction analyses, thermogravimetric analysis and magnetic susceptibility measurements were utilized to define subsolidus phase relations $\text{in air}$ for the systems cerium oxide - Ta₂O₅ and cerium oxide - Nb₂O₅. Stoichiometric CeTaO₄ is stable in air (P_O2 = 0.21 atm) only above 1265°C. At 1265°C, the reversible reaction, $\text{3}\text{CeTaO}{}_4\text{+}\text{1}\text{2}\text{?}$CeTa₃O₉ + 2CeO₂ is established. If CeTaO₄ is quenched to room temperature and $\text{reheated}$ below 1000°C, or, if the material is rapidly cooled from above 1265°C to below 1000°C it absorbs oxygen according to, . The x parameter is variable and temperature dependent. Using a thermal microbalance, three distinct complex reaction series involving a homogeneity range in x were established, (a) 0.50 ≥ × ≥ 0.48 (<350°–600°C), (b) 0.17 ≥ × ≥ 0.06 (600°–950°C), (c) 0.40 ≥ × ≥ 0.34 (950°-room temperature). CeNbO₄ (not isostructural with CeTaO₄) also absorbs oxygen below ≈700°C in air to yield CeNbO_4+x materials.     

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.     

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.     

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 $\text{“α}{}_{\mathrm{<mtext>c</mtext>}}\text{” = 5.246 ×10}{}^{\mathrm{?6}}\text{+ 6.369 ×10}{}^{\mathrm{?9}}\text{T}\text{? 7.480 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$.     

Formation of thin SiO2 films by high dose oxygen ion implantation into silicon and their investigation by IR techniques

The ion dose dependence of the infrared transmission spectra of SiO₂ layers formed by high dose ion implantation into silicon was investigated for ion doses ranging from $\text{10}{}^{16}\text{to}\text{2 × 10}{}^{18}\text{(}{}^{16}\text{O}{}_2\text{)}{}^{\mathrm{+}}\text{30}\text{kV ions cm}{}^{-2}$. The annealing temperature dependence of these spectra is also reported.The passivation properties of the SiO₂ layers and their dependence on annealing were investigated and monitored by IR techniques. It was found that an SiO₂ layer that is formed by implantation with 1 × 10¹⁸ ions cm^-2 and annealed at temperatures higher than 550 °C but not more than 800 °C is similar in its IR and passivation properties to thermally grown SiO₂ films.     

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.     

Crystal chemistry of α-(Zn,M)2V2O7 solid solutions correlation between preference for five-coordination and extension of solid solubility

Solid solutions of $\text{M}$₂V₂O₇ in α-Zn₂V₂O₇ have been prepared and equilibrated at 600°C ($\text{M}\text{=}\text{Mg, Ca, Mn, Co, Ni, Cu, Zn, and Cd}$). The crystal structure of α-Zn₂V₂O₇ contains only one type of metal site, which is five-coordinated by a somewhat distorted trigonal bipyramid ZnO₅ (Gopal & Calvo, 1973). The solubility range is largest for Cu²⁺ and Co²⁺ which can substitute for about 35% of the zinc atoms. The cations can be arranged in the following sequence with respect to their solubility in α-Zn₂V₂O₇, which accords well with these ions' preference for five-coordination:

$\text{Zn}{}^{\mathrm{2+}}\text{>> (Cu}{}^{\mathrm{2+}}\text{,Co}{}^{\mathrm{2+}}\text{) > Mg}{}^{\mathrm{2+}}\text{>(Ni}{}^{\mathrm{2+}}\text{, Mn}{}^{\mathrm{2+}}\text{) > Cd}{}^{\mathrm{2+}}$

     

On the growth of neodymium pentaphosphate crystals for laser action

The growth of Nd_xLa_1?xP₅O₁₄ (0 ≤ x ≤ 1) crystals from phosphoric acid solution has been studied. Crystals have been obtained at temperatures between 300°C and 750°C. Vitreous graphite is a suitable container for the crystal growth. Changes in crystal morphology and crystal quality with growth temperature have been observed. Evaporation at high temperatures (>550°C) in an open system is too rapid to allow the growth of high quality crystals, although large (> 1 cm) crystals may be prepared, and the best quality crystals with respect to optical inhomogeneities are prepared at 450–550°C. Both pulsed and cw laser action have been observed. The Nd³⁺${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ fluorescent lifetime increases from 120 μsec (x = 1) to μsec (sec ≤ 0.05). These values indicate a seven-fold reduction in fluorescence quenching with respect to YAG:Nd. For crystals grown at temperatures below 600°C, however shorter lifetimes are observed and the quenching becomes more severe as the temperature of preparation is lowered. The quenching may be removed by appealing low lifetime crystals at 600–700°C in a P₂O₅ atmosphere. It is proposed on the basis of infrared absorption measurements that the lifetime shortening is related to the presence of hydrogen in crystals grown at lower temperatures. The vibrational characteristics of pentaphosphate crystals have also been investigated by Raman spectroscopy.     

The growth and transformation of Pd2Si on (111), (110) and (100) Si

Thin Pd films on (111), (110), (100) and amorphous Si substrates form [001] fiber textured Pd₂Si in the temperature range 100°–700°C. The degree of texture is a function of substrate orientation, increasing in the order amorphous Si, (100) Si, (110) Si and (111) Si. Only on the (111) Si substrate is the Pd₂Si film epitaxially oriented. Temperature-dependent growth on this orientation can be characterized by [001] textured growth, epitaxial azimuth orientation at the Si interface and progressive layer by layer formation of the mosaic crystal to the thin film surface.During Pd deposition, rapid non-diffusion-controlled growth of epitaxial Pd₂Si on (111) Si occurs at substrate temperatures of 100° and 200°C. An unidentified palladium silicide of low crystallographic symmetry forms during Pd deposition onto a 50°C substrate. The diffusion-controlled growth of Pd₂Si on (111) Si follows a t^0.5 dependence. The velocity constant is

$\text{k = 7 × 10}{}^{\mathrm{?2}}\text{exp}\text{?}\text{29200±800}\text{RT}\text{cm}{}^2\text{/}\text{sec}$

Palladium deposited on 100°C (111) Ge substrates reacts during deposition to form epitaxially oriented Pd₂Ge. However, growth of this phase at higher temperatures results in a randomly oriented film. The transformation of Pd₂Ge to PdGe is kinetically controlled. After a 15 min anneal at 560°±10°C in N₂ only PdGe is detectable on (111) Ge.The high temperature stability of thin film Pd₂Si is controlled by time- temperature kinetics. For a given annealing cycle, the nucleation and growth rates of the PdSi phase are inversely related to the crystalline perfection of Pd₂Si. Decreasing transformation rates follow the order (100), (110), (111) Si. formation of thin film Pd₂Si occurs by the formation of PdSi and subsequent growth of Si within the PdSi phase. After a 30 min N₂ anneal, initial transformation occurs at 735°C on (100) Si, 760°C on (110) Si and 840°C on (111) Si. Extended high temperature annealing produces a two-phase structure of highly twinned and misoriented Si and small PdSi grains that penetrate as much as 3 μm into the Si.     

The preparation,characterisation and ion exchange properties of an amorphous titanium phosphate

An amorphous titanium phosphate has been synthesized and characterized by chemical analysis, thermal analysis (DTA and TGA), i,r. spectroscopy and X-ray diffraction of the product calcined at 1000 °C. It was assigned the molecular formula Ti₄O₂(HPO₄)₃(H₂PO₄)₂(OH)₄·3H₂O. Its exchange capacity in the processes $\text{H}{}^{\mathrm{+}}\text{Na}{}^{\mathrm{+}}$ and $\text{H}{}^{\mathrm{+}}\text{Cu}{}^{\mathrm{2+}}$ has been determined.     

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.     

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.     

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).     

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.     

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.     

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.     

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.     

Creep of mild steel at low temperatures

Creep data for mild steel at low temperatures (360–400°C) have been analysed and it has been found that the creep behaviour is similar to that at higher temperatures. The variation of secondary creep rate with stress and temperature, in the temperature range (360–538°C) may be described by two equations with a transition stress. This transition stress is 410 MPa at 360°C. For low stresses the creep equation is given by $\text{ε}{}_{\mathrm{<mtext>s</mtext>}}\text{= 250 σ}{}^{3.7}\text{exp}\text{{?(2.17 × 10}{}^5\text{/}\text{RT}\text{)}}$. Material response to stress is highly dependent on the amount of cold work; secondary creep rate decreases with increasing prior deformation.     

On the photoconductivity of heavily indium doped zinc telluride at elevated temperatures

ZnTe was prepared by solution growth from In solvents at 900°C using the THM method. The crystals resulting contained ～6 × 10¹⁹ atoms of In per cm³ and were of extremely high resistivity ($\text{> 10}{}^{10}\text{Ω-}\text{cm}$. The photoconductivity measurements at elevated temperatures revealed that the peak photosensitivity occurs at 350°C. The spectral dependence of the photoconductivity also shows some unusual features, in particular a subsidiary absorption at 630 nm which persists up to ～300°C.     

Oxygen stoichiometry in the system (CaxSr1−x)FeO3−y. Its effect on crystallographic and thermodynamic properties

Oxygen-deficient perovskites of the system (Ca_xSr_1?x)FeO_3?y were prepared at high oxygen pressures up to 1900 atm (196 MPa), and measurements were made of their crystallographic and thermodynamic behavior. The a-spacing of perovskites expanded linearly with increasing oxygen deficiency for x = 0–0.4 and y = 0.01–0.19, and an eventual tetragonal distortion took place at the composition AFeO_2.82 (64% Fe⁴⁺). Thermogravimetric analysis of SrFeO_2.81 in vacuo revealed that oxygen atoms began to release from the perovskite lattice at 350°C. Thermodynamic analysis showed that oxygen deficiency had a linear relationship with the square root of the fugacity of oxygen gas, and the slope was $\text{?1.96 × 10}{}^{\mathrm{?3}}\text{atm}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{mol}{}^{\mathrm{?1}}$.