IR Spectra of La1.85Sr0.15Cu1?xMxO4?δ(M = Zn, Ni, Mg)

Polycrystalline samples La_1.85Sr_0.15Cu_1–xZn_xO_4– (0 x 0.3), La_1.85Sr_0.15Cu_1–xNi_xO_4– (0 x 0.3), and La_1.85Sr_0.15Cu_1–xMg_xO_4– (0 x 0.3) were synthesized by the solid-state reaction method. The crystal structure and phonon vibration were investigated by means of X-ray diffraction (XRD) and infrared spectrum. Zn, Ni, and Mg doping results in the lattice parameter c decreasing and a (b) increasing. The change of the phonon modes around 504 cm^–1 and 681 cm^–1 can be satisfactorily interpreted in terms of the change of the crystal structure and the itinerant nature of charge carrier in CuO₂ sheet. The relation between the structure and phonon vibration is discussed.     

Non fermi liquid ground states in strongly correlated f-electron materials

Experimental efforts to characterize and develop an understanding of non Fermi liquid (NFL) behavior at low temperature in f-electron materials are reviewed for three f-electron systems: M_1–xU_xPd₃ (M = Sc, Y), U_1–xTh_xPd₂Al₃, and UCu_5–xPd_x. The emerging systematics of NFL behavior in f-electron systems, based on the present sample of nearly ten f-electron systems, is updated. Many of the f-electron systems exhibit the following temperature dependences of the electrical resistivity p, specific heat C, and magnetic susceptibility for T T₀, where T_o is a characteristic temperature: P(T) 1 –aT/T ₀, where a < 0 or > 0, C(T)/T (-1/T _o) In (T/bT ₀), and (T) 1 –c(T/T_o)^1/2. In several of the f-electron systems, the characteristic temperature T_o can be identified with the Kondo temperature T_k.     

Influence of Microstructure on the Strength and Cyclic Crack Resistance of Cast Irons

We study the influence of microstructure of high-strength cast irons of ferritic, ferritic-pearlitic, and pearlitic classes on the characteristics of strength and cyclic crack resistance and establish the relationship between the characteristics of strength and cyclic crack resistance and the chemical composition and microstructural parameters of the matrix and graphite inclusions of high-strength cast irons. Indeed, the ultimate strength _u = 750–850 MPa, fatigue threshold K _th = 8–10 MPa , and cyclic fracture toughness K _fc = 50–60 MPa are guaranteed by the pearlitic matrix and the following parameters of the graphite phase: the content of graphite f _p 10%, the degree of its spheroidization of about 95%, the size of globules d _gl 20–50 m, and the distance between them 40–70 m, obtained in high-strength cast irons containing (wt.%): 3.2–3.5 C, 1.9–2.5 Si, 0.35–0.4 Mn, and 0.05 Mg.     

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.     

Physicochemical Properties of R1 – xBaxMnO3 ± δ(R = Rare Earth) Solid Solutions

Nd_{1 – x} Ba _x MnO_{3 ±} (0.1 x 0.5) and R_0.7Ba_0.3MnO_{3 ±} (R = La, Pr, Sm, Eu) solid solutions were prepared from nitrate mixtures by solid-state reactions in air and were characterized by x-ray diffraction and thermogravimetry. The oxygen content of the solid solutions was determined by iodometric titration. The materials were found to have a nearly perfect oxygen stoichiometry ( 0). As shown by pH measurements, the solid solutions have a high water resistance (extent of water degradation no larger than 0.1%). The dissociation of the Nd_{1 – x} Ba _x MnO_{3 ±} (0.2 x 0.4) solid solutions was studied as a function of temperature and oxygen partial pressure (–10 log(Po ₂/Pa) 1.4) by a special TG technique.     

Superconductivity of (Y1−xREx)Ba2Cu3O7#x2212;δ system

Polycrystalline samples of the superconducting oxides (Y_1–x RE _x )Ba₂Cu₃O_7– (RE = Er and Dy) withx=0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared. From the X-ray diffraction and the electrical resistivity measurements, it was found thatT _c and the unit cell volume have common peaks nearx0.4. Close examination of previously published data on the (Y_1–xRE _x )Ba₂Cu₃O_7– system also indicate that an anomaly exists nearx–0.4. This anomaly is ascribed to an anomalous change of in oxygen nearx0.4.     

Internally Consistent Thermodynamic Description of Three-Component Liquid-Metal Systems at High Temperatures in the Entire Region of Concentration Triangle

A method is suggested for the investigation of the thermodynamic properties of ternary liquid-metal alloys at high temperatures in the entire region of concentration triangle. The method is demonstrated for a Na–K–Cs ternary system. Data are obtained for the enthalpy and Gibbs energy of formation of alloy in the temperature range of 200 T 1200 K and concentration range of 0 x _{i (j, k)} 1. The results reveal a very fine effect associated with the temperature rise, namely, the inversion of excess partial Gibbs energy G¯ _i ^*= RTln _i ( _i is the activity coefficient of the liquid component) and the change of sign of deviation of partial pressure, as well as of total pressure, from the respective values in accordance with Raoult's law. The obtained results may be used to interpret the available literature data on independent measurements of the saturation pressure.     

An apparatus for measuring the thermal conductivity and diffusivity of solid materials

An apparatus is described for measuring the thermal conductivity and diffusivity on small specimens of solid materials; also the results are shown which have been obtained for refractive high-alumina concrete by such measurements.Notation thermal conductivity at the mean temperature of specimens, W/m· °C - Q power of the central heater, W - F cross section area of a specimen, m² - t_1,2 temperature drop across the specimens, °C - ₁, ₂ difference in heights between the thermocouple beads, center-to-center, in the first and in the second specimen respectively, m - t temperature, °C - time coordinate, min - d₁= (d_1u+d_1l )/2 mean distance between specimen contact plane and nearest thermocouple beads, for the upper and lower specimen, m - d₂= (d_2u+d_2l )/2 mean distance between specimen contact plane and farthest thermocouple beads, for the upper and lower specimen, m - dt(d₁,)/d rate of temperature rise at section d₁ of the specimen at time, °C/h - t=t₁+t₂ sum of temperature drops in the specimens at time, °C - m heating rate, h^–1 - a thermal diffusivity of specimens, referred to their mean temperature, m²/h - =m/a, m^–1 b=¦(t_u–t_l)/t_u¦ heating nonuniformity factor Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1049–1054, June, 1972.     

On the measurement and physical meaning of the cleavage fracture stress in steel

Elastic-plastic two-dimensional (2D) and three-dimensional (3D) finite element models (FEM) are used to analyze the stress distributions ahead of notches of four-point bending (4PB) and three-point bending (3PB) specimens with various sizes of a C-Mn steel. By accurately measuring the location of the cleavage initiation sites, the local cleavage fracture stress _f and the macroscopic cleavage fracture stress _F is accurately measured. The _f and _F measured by 2D FEM are higher than that by 3D FEM. _f values are lower than the _F, and the _f values could be predicted by _f=(0.8––1.0)_F. With increasing specimen sizes (W,B and a) and specimen widths (B) and changing loading methods (4PB and 3PB), the fracture load P _f changes considerably, but the _F and _f remain nearly constant. The stable lower boundary _F and _f values could be obtained by using notched specimens with sizes larger than the Griffiths–Owen specimen. The local cleavage fracture stress _f could be accurately used in the analysis of fracture micromechanism, and to characterize intrinsic toughness of steel. The macroscopic cleavage fracture stress _F is suggested to be a potential engineering parameter which can be used to assess fracture toughness of steel and to design engineering structure.     

Some properties of Sb2Te3−xSex for nonvolatile memory based on phase transition

Composition dependence of properties of Sb₂Te_3–x Se _x in the range 0x<3 were studied using differential thermal analysis and X-ray diffraction. Sb₂Te_3–x Se _x form solid solution for 0<x1.25 and 2.75x<3. A systematic study of crystallization temperature in Sb₂Te_3–x Se _x (0x2.75) thin films prepared by flash evaporation was carried out. In preliminary experiments for some compositions, more than 10³ repetitions between amorphous and crystalline states were attained by the application of electric pulses.     

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

Electrical properties and phase transition of Ge1−x Sn x Se2.5 thin films

The Ge_1–x Sn _x Se_2.5 system was prepared by melting the correct ratio of high purity elements in quartz evacuated ampoules followed by quenching in ice. It was found that, within the Ge_1–x Sn _x Se_2.5 system, a glassy state can be formed when 0 x 0.4. On increasing x to 0.6 a glassy state could not be obtained, as is confirmed by X-ray diffraction. Differential thermal analysis (DTA) was carried out to study the effect of composition on the stability of amorphous phase. Ge_1–x Sn _x Se_2.5 (where 0 x 0.6) thin films have been prepared by the thermal evaporation technique. The electrical conductivity of the thin films have been studied as a function of composition and film thickness.     

Effect of Synthesis Conditions on the Lithium Nonstoichiometry and Properties of La2/3 – x Li3x □4/3 – 2x M2O6 (M = Nb, Ta) Perovskite-like Solid Solutions

The effects of the nominal composition and synthesis conditions on the lithium nonstoichiometry of La_{2/3 – x} Li_{3x 4/3 – 2x} Nb₂O₆ (I) and La_{2/3 – x} Li_{3x 4/3 – 2x} Ta₂O₆ (II) solid solutions are studied. The results demonstrate that lithium losses can be reduced from 26–30 to 14–15 mol % in system I and from 15 to 4 mol % in system II. It is shown that the disturbance of electroneutrality caused by Li nonstoichiometry in the solid solutions is eliminated via the formation of oxygen vacancies in positions O(1) (1f: 1/2 1/2 0) and O(2) (1h: 1/2 1/2 1/2) of the cation-deficient perovskite structure. The optimal lithium ion conductivity is offered by solid solutions with /3x 2.6 and x 0.136–0.143.     

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.     

Determination of the local angular radiation coefficients in certain two-body systems

A method is shown and formulas are derived by which local angular radiation coefficients can be determined in certain two-body systems where the configuration is arbitrary but one of the bodies is either a cylinder or a rectangular plate.Notation _int radiation vector of body 1 - _E ^int intrinsic radiation intensity of body 1 - _x, _y, _z components of the geometrical radiation vector along rectangular coordinates - r₀=x²+z² shortest distance from point M(x, y, z) to linear radiator - ₀ , ₀ ^' angles subtending the two segments of the linear radiator from point M(x, y, z) on area element 2 of irradiated surface - l length of the cylinders - x, y, z space coordinates of point M Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1080–1088, June, 1972.     

Investigation of the dominant point defects in tetragonal YBa2Cu3Ox at elevated temperatures

The manner in which oxygen is incorporated into YBa₂Cu₃O _x (YBCO) at 800°C for values ofx close to 6 is shown to be in the form of neutral oxygen interstitials, O _i ^x . The experimental data on which this conclusion is based are obtained from measurements of oxygen partial pressure,P(O₂), as a function of compositionx and temperatureT (5.99x 6.35, 825T1120 K). The data are obtained by a solid-state electrochemical method. Other conclusions of this study include: (a) O _i ^x are noninteracting forx 6. (b) The stoichiometric composition of YBCO isx 6.0. (c) The reaction enthalpy of oxidation is 179 kJ/mol O₂. (d) The Fermi level changes by –0.2 eV asx increases from 6.05 to 6.35.     

Synthesis, Structure, and Properties of Ammonium Polyvanadomolybdate Xerogels

Powders and films of (NH₄)_{2 – x} H _x V_{12 – y} Mo _y O_{31 ±} · nH₂O (0 x 2, 0 y 3) xerogels with a layered structure were prepared for the first time. According to IR spectroscopy data, the V–O–Mo layers in the xerogels are similar to those in the delta vanadium bronze (NH₄)_0.5V₂O₅. X-ray photoelectron spectroscopy shows that the vanadium and molybdenum in the xerogels are mainly in the oxidation states 5+ and 6+, respectively. The materials also contain small amounts of V⁴⁺and OH^–. The thermal stability of the materials increases with Mo content. The electrical conductivity of the films depends on air humidity and reaches a maximum at the composition (NH₄)_1.5H_0.5V₉Mo₃O_{31 +} · nH₂O. At temperatures in the range 20–70°C and air humidity between 12 and 59%, the activation energy of conduction is very low.     

Magnetic field dependence of zero-sound attenuation close to the pair-breaking edge in3He-B due toJ=1−,J z =±1 collective modes

Our previous theory yielded for the Zeeman splitting of the imaginaryJ=1 collective mode in³He-B the result =2+0.25J _z ( is the effective Larmor frequency). In this paper we take into account the downward shift of the pair-breaking edge from 2 to 2₂– (₂ and ₁ are the longitudinal and transverse gap parameters). This leads to a complex Landé factor: the frequencies of theJ _z =±1 components become =2+0.39J _z , and the linewidths of these resonances become finite: =0.18. The coupling amplitudes of theJ _z =±1 components to density are found to be proportional to gap distortion, (₁–₂/(/)². Our results for the ultrasonic attenuation due to theJ _z =±1,J=1 modes are capable of explaining the field dependence of the attenuation close to the pair-breaking edge as observed by Dobbs, Saunders, et al. The observed peak is caused by theJ _z =–1 component: its height increases due to gap distortion as the field is increased, and the peak shifts downward in temperature and its width increases with the field due to the complex Landé factor. TheJ _z =+1 component gives rise to a corresponding dip relative to the continuum attenuation.     

Nuclear ferromagnetic ordering of141Pr in the diluted Van Vleck paramagnets Pr1−x Y x Ni5

We report on the first investigation of the effect of magnetic dilution on nuclear magnetic spin interactions in metals; we studied this effect in the diluted Van Vleck paramagnets Pr_1–xY_xNi₅. In addition, we investigated the electronic magnetic properties of these intermetallic compounds. For this purpose, we have measured the nuclear and electronic susceptibilities of Pr_1–xY_xNi5 with x = 0 to 0.2 at 50K T 8 mK and at 2.2 K T 300 K. We observe a linear decrease of the electronic Van Vleck susceptibility and of the hyperfine enhancement factor by 13% (per mole Pr³⁺). The hyperfine-enhanced nuclear susceptibility decreases by about a factor of three when going fromx = 0 tox = 0.2. The samples show nuclear ferromagnetic transitions of¹⁴¹Pr with nuclear Curie temperatures T_c decreasing from 370 K to 100 K and Weiss temperatures decreasing from 218 K to 13 K in this concentration range. These data are compared with the results of mean-field calculations. In addition, we report on measurements of the nuclear spin relaxation time of these compounds, for which we find values of a few msec at millikelvin temperatures and a critical speeding-up at T_c. Our data give hints that for x > 0.2 the character of the nuclear magnetic transition may change, possibly to a nuclear spin glass freezing.