Influence of Argon on the Phase Behavior and Vibrational Properties of Solid Nitrogen at High Pressure

The mixed solid N ₂–Ar has been studied at high pressure at the nitrogen–rich side of the phase diagram by Raman spectroscopy. The argon atoms dissolve into some of the nitrogen structures. Within the *–phase the Ar–-atoms are mainly located at the sphere–like disordered sites in agreement with computer simulations. The second order transition of pure N ₂ is still present in the mixed solid at 25 mole% Ar. The * – * and *–fluid transitions in the mixed solid are shifted compared to the pure system. The phase diagram of the mixture for x[N ₂]0.75 has been studied.     

Oxygen Stoichiometry and Phase Transitions of SrCo1– xFexO3 – δ

The oxygen stoichiometry of SrCo_{1 – x} Fe _x O_{3 –} (0.1 x 0.9) solid solutions was determined by solid-electrolyte coulometry as a function of temperature (20–1000°C) and oxygen partial pressure (1–100 Pa). The results, together with X-ray diffraction studies between 400 and 900°C, indicated a sequence of phase transitions: perovskite brownmillerite high-temperature perovskite. The composition stability region of the parent perovskite structure was shown to be 0.2 <x 1.0. The Co-rich samples (x 0.2) consisted of perovskite and hexagonal phases.     

Growth and Properties of V-Doped CdxHg1 – xTe Crystals

Cd _x Hg_{1 – x} TeV (x= 0.9–0.95) crystals were prepared by two versions of Bridgman growth, and their optical homogeneity and transport properties were studied. The electrical resistivity of the crystals was 10⁴to 10⁸ m. From the temperature dependences of the Hall coefficient, the activation energy of the vanadium level in Cd _x Hg_{1 – x} TeV was determined to be 0.73–0.82 eV.     

Phase Relations in the SrO–Bi2O3–Fe2O3 System

The phase relations in the composition region SrFeO_{3 –} –Fe₂O₃–BiFeO₃ are studied in air by x-ray diffraction and electron microscopy. The 1000°C phase compatibility diagram is constructed. Sr_{1 – x} Bi _x FeO_{3 –} solid solutions are prepared in the range 0 < x 0.8. Their lattice parameter is found to vary nonlinearly with x. Two new phases were identified: (Sr,Bi)₃Fe₄O _y (tetragonal lattice, a= 3.907(2) Å, c= 27.30(2) Å) and Sr_0.6Bi_0.4FeO_{3 –} (tetragonal lattice,a = 5.555(2) Å, c= 11.848(5) Å).     

Dielectric and Piezoelectric Properties of NaNbO3-Based Solid Solutions

Detailed data are presented on the structure and electrical properties of Na_{1 – x} Li _x NbO₃ (0 x 0.145), Na_{1 – x} K _x NbO₃ (0 x 1.0), and (Na_{1 – x} Pb _x )(Nb_{1 – x} Ti _x )O₃ (0 x 1.0) solid solutions prepared by solid-state reactions followed by hot pressing. The sequences of phase changes and the stability ranges of the resulting phases are identified. The results are used to map out the compositional phase diagrams of the NaNbO₃-based binary systems.     

High pressure synthesis and electrical properties of BaTiO3−xFx

The substitution of fluorine for oxygen in BaTiO₃ was investigated by the reaction of BaO₂, BaF₂, TiO₂ and Ti under the conditions of 3.0 GPa and 1300° C for 2 H. Batio_3–x F _x solid solutions were obtained as a single phase in the region of 0 x0.1. The X-ray diffraction data showed that the symmetrical change from tetragonal to cubic form occurred atx=0.08 at room temperature. Also, the solid solutions were characterized by TG-DTA analysis, ESCA spectroscopy and diffusion reflectance spectroscopy. As a result, the existence of Ti³⁺ was verified. The electrical resistivities of BaTiO_3–x F _x were in the range from 4cm for x=0.05 to 3Ocm forx=0.1 at 300 K and the relationship between In and 1000 T^–1 was linear. The thermoelectric powers at 300 K were –250V K^–1 forx=0.05 and –130VK^–1 forx=0.1. The electrical property of the solid solution was discussed on the basis of a conventional band model which involved localized donor levels associated with oxygen vacancies.     

Preparation of LiTaO3 , LiNbO3 , and NaNbO3 from Peroxide Solutions

A procedure is described for preparing peroxide solutions of LiTaO₃ and LiNbO₃. It is shown that the use of peroxide solutions makes it possible to obtain stoichiometric LiTaO₃, LiNbO₃, and NaNbO₃ and Li _x Na_{1 – x} Nb₃ solid solutions.     

Ionic conductivity and crystal structure relationships in Ti/Cu substituted Bi4V2O11

Crystal structure and oxide ion conductivity of a series of Ti and Ti-Cu double substituted Bi₄V₂O₁₁ compounds, Bi₂V_(1–x)Ti _x O_(11–x)/2 (0.085 x 0.15), and Bi₂V_0.9Cu_(0.1–x)TixO_5.35+x (0 x 0.1), were investigated using X-ray powder diffraction and ac impedance spectroscopy in the temperature and frequency range of 100–700°C and 10^–2–10⁷ Hz, respectively.Structural phase transitions, and , occur as a function of composition in Ti substituted compounds for which the is evidenced to be stable at room temperature when x exceeds 0.125. For all Ti-Cu double substituted compounds studied, the room temperature phase was identified to be phase.The required amount of Ti for phase stabilization at room temperature was significantly reduced and the conductivity improved when Cu substituted a part of Ti. Therefore, for the Bi₂V_0.9Cu_(0.1–x)Ti _x O_5.35+x (0 x 0.075) compounds the ionic conductivity increased and activation energy decreased with decreasing x. At low temperature, the highest ion conductivity was obtained for Bi₂V_0.9Cu_0.1O_5.35. At high temperature (T>500°C), a different behavior was observed. The total conductivity increased at first with decreasing x values down to x = 0.05 and then decreased. The maximum conductivity was obtained for Bi₂V_0.9Cu_0.05Ti_0.05O_5.4, and the activation energy decreased with decreasing x values, such as what happened at low temperature.     

Chebyshev approximation for the roots of the equation BiWГ(μ)=μVГ(μ)

A minimax approximation, uniform for Bi [0, ), is developed for the roots of the equation BiW()=V(), by means of Chebyshev polynomials.Translated from Inzhenero-Fizicheskii Zhurnal, Vol. 28, No. 4, pp. 710–715, April, 1975.     

Fatigue of metallic glasses

The fatigue behaviour of Ni₄₉Fe₂₉P₁₄B₆Si₂, Ni₄₈Fe₂₉P₁₄B₆Al₃ and Pd_77.5Cu₆Si_16.5 metallic glasses is examined. In the finite lifetime regime the relationship between stress amplitude ( _a), fracture stress ( _f), mean stress ( _m) and cycles to failure (N _f) is _a=A( _f–_m) (2N _f) ^b , whereA andb are 16.9 and –0.40 respectively for reduced gauge section Ni₄₉ strips (for _m 140 kg mm^–2) and 27.0 and –0.44 for Pd base wires. These results are unusual in thatA 1. Consequently, a sharp discontinuity exists near _a( _f– _m) –1. In a simple tensile test failure occurs at _f(=_y) and 2N_f=1; for peak stresses only a percent or so less than _f the sample will withstand hundreds of cycles of stress. For uniform cross-section glassy metal filaments, a fatigue limit is observed at stress ratios ( _a/ _f) in the vicinity of 0.07 to 0.15. The fatigue limit for reduced section specimens is a factor of 2 higher. Fatigue failure of the Ni-Fe strips may occur under partially or fully plane stress or plane strain conditions, depending on sample thickness and stress. Final failure of the Pd_77.5Cu₆Si_16.5 wires always occurs by general yielding of the remaining section.     

Low-temperature specific heat of YBa2Cu3O7, YBa2Cu3O6, Y2BaCuO5, YBa3Cu2O7, BaCuO2, and CuO

We have measured the low-temperature specific heat (1.3T20 K) and the dc magnetic susceptibility (100T250 K) of eight samples of the high-T _c superconductor Y _x Ba_3–x Cu₃O_7– (x=0.9, 1.0, 1.1) and of two samples of nonsuperconducting YBa₂Cu₃O₆₊. We have also performed specific heat measurements on the possible impurity phases: YBa₃Cu₂O₇, Y₂BaCuO₅, CuO, and BaCuO_2+x . The superconducting samples all have a nonzero, sample-dependent linear term * and an upturn inC/T at very low temperature. We show that this anomalous behavior is at least partly due to the presence of a small amount (1%) of BaCuO_2+x impurity phase in the measured samples. This is evidenced by the correlation between * and the Curie component of the susceptibility, which is proportional to the amount of paramagnetic impurities.     

Supercooling of In2Bi and InBi Melts

The effect of melt overheating T ⁺ on the critical supercooling T ^– of liquid In₂Bi and InBi is studied by cyclic thermal analysis. It is shown that, the T ^– for In₂Bi is 2.0 K, independent of the melt preheating temperature. In contrast, the T ^– for InBi varies jumpwise with T ⁺: T ^– 1.0–1.6 K at T ⁺ < 5 K, and T ^– 16 K at T ⁺ = 5–300 K, independent of the cooling rate (varied from 0.002 to 8.0 K/s). The solidification behaviors of In₂Bi and InBi are shown to correlate with the structures of their liquid and solid phases.     

Phase equilibria at 1100°C in air and crystal structure of solid solutions in the system LaCoO<Subscript>3</Subscript>—SrCoO<Subscript>2.5</Subscript>—“SrNiO<Subscript>3</Subscript>”—“LaNiO<Subscript>3</Subscript>”

Phase equilibria in the LaCoO₃—SrCoO_2.5—SrNiO₃—LaNiO₃ system are studied at 1100°C in air using samples prepared by standard solid-state reactions and by the citrate route. The composition region and structure of La_{1 – x}Sr_xCo_{1 – y}Ni_yO_{3 –} solid solutions are determined by x-ray powder diffraction. The structure is refined by the Rietveld profile analysis method with Fullprof 2002. The solid solutions with 0< x 0.5 have a rhombohedrally distorted perovskite structure (sp. gr.R c). The rhombohedral distortion decreases with increasing Sr content, and the solid solutions with x > 0.5 have an ideal cubic structure (sp. gr. Pm3m). The composition dependences of lattice parameters for the La_{1 – x}Sr_xCo_{1 – y}Ni_yO_{3 –} solid solutions are presented.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1520–1525.Original Russian Text Copyright © 2004 by Aksenova, Gavrilova, Cherepanov.     

d-Hole localization and the suppression of superconductivity in YBa2(Cu1-xZnx)3O7?y

The temperature and Zn concentration dependence of the electrical resistivity, specific heat, magnetic susceptibility, and electron paramagnetic resonance (EPR) spectra of YBa₂(Cu_1–x Zn _x )₃O_7–y withy0.1 has been measured forx0.16. In addition, the temperature and field dependence of the magnetization has been measured for 2<T<300K and 0<H<9.0T, along with the temperature and quasihydrostatic pressure dependence of the electrical resistivity for selected samples for 0<P<13 GPa. The substitution of Zn for Cu in YBa₂Cu₃O_7–y causes a rapid and nearly linear depression of the superconducting transition temperature,T _c , withT _c going to 0 K forx 0.10. YBa₂(Cu_1–x Zn _x )₃O_7–y retains the YBa₂Cu₃O_7-y orthorhombic structure forx0.16 for both the superconducting and nonsuperconducting samples. Initially, the unit cell volume increases nearly linearly with Zn content; however, an abrupt change occurs in the vicinityx=0.8–0.10. Forx<0.10, the temperature dependence of the electrical resistivity,(T), is metallic-like (d/dT>0) and increases gradually with increasing Zn content. However, forx 0.10,(T) becomes semiconductor-like, with a very rapid increase of the resistivity with increasingx. The electrical resistivity, magnetic susceptibility, EPR spectra, and specific heat all indicate that thed-holes associated with the Cu ions become localized in the nonsuperconducting phase,x>-0.10.     

Structure and Diamagnetic Properties of (Pb0.6SnyCu0.4 ? y)Sr2(Y1 ? xCax)Cu2Oz

The effect of Sn doping in (Pb_0.6Sn _y Cu_{0.4 – y} )Sr₂(Y_{1 – x} Ca _x )Cu₂O _z with 0 y 0.3 and 0 x 0.7 was investigated. It was established that a nearly pure 1212 phase can be obtained at 0 y 0.1 and 0 x 0.3. The obtained XRD patterns as well as the results of the EDX and ICP-AES analyses showed that Sn substitution is possible in the (Pb,Cu)-1212 phase. Superconductivity was observed at 0.4 x 0.7. The onset of the diamagnetic transitions varied from 10 to 30 K. The influence of the strong Pb deficiency on the superconducting properties of the samples was discussed.     

Crystallization kinetics in glassy Ge20Se80−x In x alloys

Crystallization kinetics is studied in glassy Ge₂₀Se_80–xIn_x (0 x 20) using isothermal annealing at temperatures between the glass transition and melting. D.c. conductivity is taken as a parameter to estimate the extent of crystallization (). The activation energy of crystallization (E) and the order parameter (n) are calculated by fitting the values of in the Avrami equations of isothermal crystallization. The results indicate that E is highly composition-dependent, which is explained in terms of the stable phases in the Ge-Se-In system.     

Equation of state of3He near its liquid-vapor critical point

We report high-resolution measurements of the pressure coefficient (P/T) for³He in both the one-phase and two-phase regions close to the critical point. These include data on 40 isochores over the intervals–0.1t+0.1 and–0.2+0.2, wheret=(T–T _c )/T _c and =(– _c )/ _c . We have determined the discontinuity (P/T) of (P/T) between the one-phase and the two-phase regions along the coexistence curve as a function of . The asymptotic behavior of (1/) (P/T) versus near the critical point gives a power law with an exponent (+–1)^–1=1.39±0.02 for0.010.2 or–1×10 ^–2t–10 ^–6 , from which we deduce =1.14±0.01, using =0.361 determined from the shape of the coexistence curve. An analysis of the discontinuity (P/T) with a correction-to-scaling term gives =1.17±0.02. The quoted errors are fromstatistics alone. Furthermore, we combine our data with heat capacity results by Brown and Meyer to calculate (/T) _c as a function oft. In the two-phase region the slope (²/T ²)_c is different from that in the one-phase region. These findings are discussed in the light of the predictions from simple scaling and more refined theories and model calculations. For the isochores 0 we form a scaling plot to test whether the data follow simple scaling, which assumes antisymmetry of – ( _c ,t) as a function of on both sides of the critical isochore. We find that indeed this plot shows that the assumption of simple scaling holds reasonably well for our data over the ranget0.1. A fit of our data to the linear model approximation is obtained for0.10 andt0.02, giving a value of =1.16±0.02. Beyond this range, deviations between the fit and the data are greater than the experimental scatter. Finally we discuss the (P/T) data analysis for ⁴ He by Kierstead. A power law plot of (1/) P/T) versus belowT _c leads to =1.13±0.10. An analysis with a correction-to-scaling term gives =1.06±0.02. In contrast to ³ He, the slopes (²/T ²)_c above and belowT _c are only marginally different.Work supported by a grant from the National Science Foundation.     

Thermomechanic behavior of a polymer upon its formation in a crystallization process: Theoretical principles,hypotheses, and mathematical model

A model of thermomechanic behavior of a polymer upon its formation in a crystallization process is proposed. Based on methods of nonequilibrium thermodynamics governing relationships are obtained which make it possible to establish the dependence of the final degree of crystallicity of the material on the history of the crystallization process and to explain the mechanism of formation of the remanent stresses in a polymer article.Notation u translation vector - v velocity vector - acceleration vector - absolute temperature - density - c specific heat capacity - deformation tensor - strain tensor - specific enthropy - U ^* internal energy - z specific free enthalpy - _i internal parameters of state - t time - q heat flux vector - matrix of heat conduction coefficients - W ^* energy dissipation - F vector of mass forces - the 4th rank tensor of elastic pliabilities - matrix of heat expansion coefficients - tensor of contribution of structural variations to deformation - function of equilibrium value ^* - p mean pressure - deviator of the tensor of deformations - spherical part of the deformation tensor - deviator of the tensor of stresses - K volume modulus - unity tensor - Q enthalpy of the crystallization process - Q _eq enthalpy of the equilibrium crystallization process - _g glass transition temperature - ^*() the curve obtained in the equilibrium crystallization process - f final degree of crystallicity Institute of Mechanics of Continuous Media of the Ural Branch of the Russian Academy of Sciences, Perm', Russia. Institute of Technical Chemistry of the Ural Branch of the Russian Academy of Sciences, Perm', Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 479–485, May–June, 1995.     

Compressibility measurements of β- and β″ -alumina

The compressibilities of the a- and c-axes for sodium - and -aluminas were determined up to 10 GPa from the pressure dependence of powder X-ray diffraction measured at room temperature using synchrotron radiation as an X-ray source. Powders of sodium - and -aluminas which were prepared from grinding synthesized single crystals were used as the specimens for X-ray diffraction. The compressibilities of - and -aluminas are 1.5 ± 0.2 ×10^–12 and 1.7 ± 0.2 × 10^–12 Pa^–1 for the a-axis and 2.9 ± 0.2x10^–12 and 1.6 ± 0.2 ×10^–12 Pa^–1 for the c-axis, respectively. For the c-axis, the compressibility of -alumina is larger than that of -alumina. This experimental fact is explained by the different stacking of oxygen layers and the different content in sodium ion between - and -aluminas.     

Ultrasonic propagation in solid H2: The effects of orientational ordering

A report is given of the observation below 1 K of the sound attenuation expected from progressive orientational ordering in hcp H₂ with ortho concentrationsX<0.53. The experiments were carried out at 10 and 30 MHz. The amplitude of this effect depends on the coupling between the lattice vibrations and the molecular orientation, and should be maximum when the acoustic angular frequency is comparable with the orientational relaxation rate ^–1. The average rate can be roughly estimated from NMR longitudinal relaxation timeT ₁ measurements. Such a maximum for was indeed observed in the expected temperature range. At high enough temperatures, was found to be proportional toT ₁ ^–1 . which is consistent with predictions in the high temperature limit. Furthermore, the transition between the hcp and the fcc phases forX>0.53 is studied by means of the large changes in the sound propagation at the transition, and the phase diagram thus obtained is compared with results from x-ray and pressure measurements. The new observations explain some previous discrepancies in results using different methods. The difference between solid H₂ and D₂ regarding the stabilization of the cubic structure above the orientational ordering transition is also discussed. Calculations of the respective energy barriers E to be overcome during the martensitic transition are suggested.