Thermodynamic properties of NaZr<Subscript>2</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The heat capacity C _p ⁰ of crystalline NaZr₂(AsO₄)₃ has been measured in the range 7–650 K using precision adiabatic calorimetry and differential scanning calorimetry. The experimental data have been used to calculate the standard thermodynamic functions of the arsenate: C _p ⁰, enthalpy H ⁰(T) − H ⁰(0), entropy S ⁰(T), and Gibbs function G ⁰(T) − H ⁰(0) from T → 0 to 650 K. The standard entropy of its formation from elements is Δ_f S ⁰(NaZr₂(AsO₄)₃, cr, 298.15 K) = −1087 ± 1 J/(mol K).     

Thermodynamic properties of Cu<Subscript>5</Subscript>SmSe<Subscript>4</Subscript>

The heat capacity of Cu₅SmSe₄ has been measured from 80 to 300 K. The results have been used to assess the main thermodynamic functions of Cu₅SmSe₄: entropy (S ⁰(T) − S ⁰(0)), enthalpy increment (H ⁰(T) − H ⁰(0)), and reduced Gibbs energy (Φ⁰(T)).     

Thermodynamic functions of ScVO<Subscript>4</Subscript> at temperatures from 0 to 350 K

The heat capacity of ScVO₄ has been determined by adiabatic calorimetry at temperatures from 14.52 to 347.13 K, and smoothed heat capacity data have been used to evaluate its thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy). At 298.15 K, the thermodynamic functions of scandium orthovanadate are C _p ⁰(298.15 K) = 110.5 ± 0.1 J/(mol K), S ⁰(298.15 K) = 110.9 ± 0.1 J/(mol K), H ⁰(298.15 K) − H ⁰(0) = 18.53 ± 0.01 kJ/mol, and Φ⁰(298.15 K) = −[G ⁰(298.15 K)/298.15] = 48.75 ± 0.12 J/(mol K). The calculated Gibbs energy of formation of scandium orthovanadate from its constituent elements is Δ_f G ⁰(ScVO₄, 298.15 K) = −1644.0 ± 2.2 kJ/mol.     

Heat capacity and thermodynamic functions of LaVO<Subscript>4</Subscript> and LuVO<Subscript>4</Subscript> from 7 to 345 K

The heat capacities of lanthanum and lutetium orthovanadates have been measured at temperatures from 7 to 345 K using an adiabatic calorimeter. No anomalies have been detected in the heat capacity data. The thermodynamic functions (C _p ⁰(T), S ⁰(T), and H ⁰(T) − H ⁰(0)) of the two compounds have been calculated in the temperature range studied, and their Debye characteristic temperatures have been estimated.     

Composition range and thermodynamic properties of Tl<Subscript>5</Subscript>Se<Subscript>2</Subscript>Br-based solid solutions

The equilibrium subsolidus phase diagram of the TlBr-Tl₂Se-TlSe system has been mapped out using X-ray diffraction analysis and emf measurements on thallium concentration cells. Tl₅Se₂Br has been shown to have a broad homogeneity region. The emf results are used to evaluate the relative partial thermodynamic functions of the thallium in the alloys studied and the standard integral thermodynamic functions (ΔG ⁰(298 K), ΔH ⁰(298 K), S ⁰(298 K)) of the Tl₅Se₂Br-based solid solutions.     

Low-temperature magnetoresistance of biaxially strained 24-nm-thick La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films

The lateral unit cell parameter in nanodimensional La_0.67Ca_0.33MnO₃ (LCMO) films grown on (001)-oriented LaAlO₃ substrates is significantly (approximately 4%) smaller than the value measured along the normal to the substrate plane. At T < 140 K, the temperature dependence of the resistivity ρ of LCMO films follows the relation ρ − ρ (T = 4.2 K) ≈ρ₂(H)T ^4.5, where ρ₂ is independent of the temperature but decreases with increasing magnetic field H. It is shown that this decrease is related both to a decay of the spin waves in ferromagnetic domains and to the transformation of antiferromagnetic phase inclusions into ferromagnetic ones.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

Impact of Tuning Molar Ratio in the Starting Materials: <Emphasis Type="Italic">Magneto</Emphasis>-Transport Features of Hybrid YSr<Subscript>2</Subscript>Ru<Subscript>0.9</Subscript>Cu<Subscript>2.1</Subscript>O<Subscript>7.9</Subscript>

The impact of slightly tuning molar ratio in the starting materials on the physical properties of 1212-type rutheno-cuprate, YSr₂Ru_0.9Cu_2.1O_7.9 (nominal) samples prepared under four synthesis approaches are reported. Interestingly, all samples clearly show the differences in the physical properties of the samples prepared under different synthetic protocols. However, neither XRD nor EDX reveal any notable differences in the crystal structure or sample composition. All the samples exhibit magneto-superconducting properties (H _ext=5 Oe) which are slightly varied with synthetic approaches. The high field (H _ext=10 kOe) temperature dependence of magnetization data shows a sharp ferromagnetic transition around 150 K and all the samples obey Curie–Weiss linear behavior above 180 K. The experimental effective paramagnetic moment for the various samples is in the range of 2.5 and 2.7μ _B/Ru which are in line with the literature report. The magnetization, M(H) isotherm curves measured at 5 K and −10 kOe≤H≤10 kOe conditions reveal weak ferromagnetic-like hysteresis loops for all samples with returning moment (M _r) and coercive field (H _c), whereas the high field M(H) loops indicate soft ferromagnetic behaviors with magnetic saturation. The saturation moment of the samples is slightly varied with the synthesis approaches. None of the samples showed bulk superconductivity (T_c^{R = 0})T_{\mathrm{c}}^{R = 0}) down to 2 K, while all samples show onset transitions (T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}}) except the sample prepared by approach-3. The latter approach sample shows semiconducting behavior down to 2 K. The T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}} noticed at 34 K, 12 K, and 6 K for the sample prepared by approach-1, 2, and 4, respectively. The nearly linear dependence suggests that hopping conduction is dominant in certain temperature range for all samples. The magneto-transport features of these samples exhibit maximum magnetoresistance (MR) at low temperatures. Remarkably, the sample prepared by approach-1 shows largest −MR about 77% at low temperature 2 K and H=90 kOe which stimulates for further investigations. Among the four synthesis approaches employed in the present study, we can probably suggest that the approach-1 (0.5Y₂O₃+0.5SrO₂+1.5SrCuO₂+0.9RuO₂+0.6CuO) is the preferable method to achieve the best sample (in terms of magneto-transport features).     

Scaling of the Temperature Dependent Resistivity and Hall Effect in Ba(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)As<Subscript>2</Subscript>

We show that the temperature-dependent resistivity ρ(T), Hall number n _H(T) and the cotangent of the Hall angle cot θ _H(T) of Ba(Fe_1−x Co _x )As₂ (x=0.0–0.2) can be scaled using a recently proposed model-independent scaling method (Luo et al. in Phys. Rev. B 77:014529, 2008). The zero field normal-state resistivity above T _c can be reproduced by the expresion r(T) = r₀ +cTexp(- \frac2\varDelta T )\rho(T) = \rho_{0} +cT\exp(- \frac{2\varDelta }{T} ) and scaled using the energy scale Δ, c and the residual resistivity ρ ₀ as scaling parameters. The scaling parameters have been calculated and the compositional variation of 2Δ and ρ ₀ has been determined. The 2Δ(x) dependence show almost linear decreasing in underdoped regime, minimum corresponding to the T _c maximum and increasing in overdoped regime. The latter is different from that reported for cuprates. The existence of a universal metallic ρ(T) curve which, however, is restricted for the underdoped compounds to temperatures above a structural and antiferromagnetic transition is interpreted as an indication of a single mechanism which dominates the scattering of the charge carriers in Ba(Fe_1−x Co _x )As₂ (x=0.0–0.2).     

Electrical properties of Y-modified Pb(SnTi)O<Subscript>3</Subscript> ferroelectric ceramics

Y-modified Pb(SnTi)O₃ polycrystalline materials with a general formula (Pb (Sn (PYST) (x = 0, 0.05, 0.07, 0.1) have been synthesized using the standard mixed oxide method. Crystallographic and surface morphology studies are carried out by the powder X-ray diffraction and scanning electron microscopy techniques. X-ray diffraction studies of the samples showed the tetragonal structure of the unit cell. Uniform grain distributions with porosity throughout the surface of the sample pellets are observed. The T _C (transition temperature) increases with increase in the mole fraction of the substituent (x). ɛ^/ _max is found to decrease with increase in x. The slope of lnσ_ac∼ 1/T shows distinct variations for temperature below 410 K, 410 K to T _c and for T > T _c. The room temperature ac conductivity at 10 kHz lies in the range of 10⁻⁵–10⁻⁶ (ohm⁻¹ m⁻¹).     

Formation and properties of SnO–MgO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

A new glass system SnO–MgO–P₂O₅ with low viscosity has been developed by a melt-quenching method. Formation, thermal properties, and chemical durability of these glasses have been investigated. For a constant P₂O₅ concentration, the glass formation ability is enhanced with the increasing Sn/(Sn + Mg) ratio. The glasses exhibit low glass transition temperature (T _g = 270–400 °C), low dilatometric softening temperature (T _DS = 290–420 °C), and high thermal expansion coefficient (CTE = 110–160 × 10⁻⁷ K⁻¹). With the increasing Sn/(Sn + Mg) ratio, T _g and T _DS decrease, and CTE increases. When Sn/(Sn + Mg) ratio is varied, the relationship between chemical durability and thermal properties of the present glasses is not consistent with what expected in general cases. It is noted that the glasses with 32–32.5 mol% P₂O₅ exhibit excellent chemical durability and tunable T _g, T _DS, and CTE (by varying Sn/(Sn + Mg) ratio).     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.     

Synthesis and structural studies of Na<Subscript>2</Subscript>O-ZnO-ZnF<Subscript>2</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> oxyfluoride glasses

This paper describes the synthesis and spectroscopic studies of the glass system, 20Na₂O-(20-x) ZnO-xZnF₂-60B₂O₃(x = 0, 5, 10, 15, 20), prepared by melt quenching method. The analyses of DSC and XRD did not show the crystallinity of the glass sample. ¹¹B MAS-NMR shows the presence of sharp peak around −14 ppm. From the IR studies, the broadening of the peak around 1200–1400 and 800–1100 cm⁻¹ shows the presence of mixed linkages like B-O-B, B-O-Zn in the network.     

Measurements of thermophysical properties of molten silicon by a high-temperature electrostatic levitator

Several thermophysical properties of molten silicon measured by the high-temperature electrostatic levitator at JPL are presented. They are density, constant-pressure specific heat capacity, hemispherical total emissivity, and surface tension. Over the temperature range investigated (1350<T _m<1825 K), the measured liquid density (in g·cm⁻³) can be expressed by a quadratic function,p(T)=p _m−1.69×10⁻⁴(T−T _m)−1.75×10⁻⁷(T−T _m)² withT _m andp _m being 1687 K and 2.56 g·cm⁻³, respectively. The hemispherical total emissivity of molten silicon at the melting temperature was determined to be 0.18, and the constant-pressure specific heat was evaluated as a function of temperature. The surface tension (in 10⁻³ N·m⁻¹) of molten silicon over a similar temperature range can be expressed by σ(T)=875–0.22(T−T _m). Invited paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.      

Spectroscopic studies of TeO<Subscript>2</Subscript>–ZnO–Er<Subscript>2</Subscript>O<Subscript>3</Subscript> glass system

Series of glass based on the (80 − x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ≤ x ≤ 2.5 mol%) has successfully been made by melt quenching technique. The optical properties of glass have been investigated by means of IR and Raman spectroscopy. It is observed that as the Er₂O₃ content is being increased, the sharp IR absorption peaks are consistently shifted from 650 to 672 cm⁻¹ while the Raman shift intensity around 640–670 cm⁻¹ is decreases but increases around 720–740 cm⁻¹. It is found out that both phenomenons are related to the structural changes between the stretching vibration mode of TeO₄ tbp and TeO₃ tp, and bending vibration mode of Te–O bonds in the glass linkages.     

Electrical conduction properties of Sr-doped Bi<Subscript>4</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>3</Subscript> with the eulytite-type structure

Electrical conduction in 1 mol% Sr-doped Bi₄(SiO₄)₃ with the eulytite-type structure at elevated temperatures was investigated with conductivity measurements. Conductivity of the material under wet condition was higher than that under dry condition, and were 1.2 × 10⁻⁶ – 9.7 × 10⁻⁵ S cm⁻¹ at 500–850 ^°C. From H/D isotope effects and p(O₂)-dependencies of the conductivity, it was found that the Sr-doped Bi₄(SiO₄)₃ exhibited protonic conduction at all the temperatures investigated while contribution of p-type conduction became significant with increasing p(O₂) and/or temperature. Protonic and p-type conductions in the material were discussed in terms of defect equilibria.     

Reduction of Np(V) with Fe(II) in weakly acidic solutions containing H<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The kinetics of the reaction of Np(V) with Fe(II) in dilute perchloric and nitric acid solutions containing H₂C₂O₄ was studied by spectrophotometry. In the range pH 1–2, the reaction rate is described by the equation d[Np(V)]/dt = k[Np(V)][Fe(II)][H₂C₂O₄]²[H⁺]^−1.6, k = 182 mol^−1.4 l^1.4 s⁻¹. The activation energy in the range 25–45°C is 26 kJ mol⁻¹. The reaction mechanism involves formation of Fe(II) and Np(V) oxalate complexes, followed by their reaction with the participation of the H⁺ ion.     

A study on electrodeposited Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

Zn_1−x Fe _x alloys were electrochemically deposited on AISI 4140 steel substrates from sulfate bath. The bath was consisted of 40 g dm⁻³ ZnSO₄·7H₂O, 20–40 g dm⁻³ FeSO₄·7H₂O_, 25 g dm⁻³ Na₃C₆H₅O₇, and 16 g dm⁻³ H₃BO_3. The effect of bath composition on the electrical resistivity, the phase structure, and the corrosion behavior were investigated by the current–voltage measurements versus temperature, the X-ray diffraction (XRD) analysis, the atomic absorption spectrometry analysis, and the polarization measurements, respectively. Iron content was shown to strongly affect the structure, the electrical resistivity and the corrosion stability of Zn–Fe alloys.     

Synthesis and characterization of LiNi<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>O<Subscript>2</Subscript> for lithium batteries

LiNi_0.9Co_0.1O₂ cathode material is prepared from LiOH·H₂O and Ni_0.9Co_0.1(OH)₂ by co-precipitation and subsequent two-stage heat treatment in flowing oxygen based on the results of thermogravimetric. The structural and electrochemical properties of the samples are characterized by means of inductively coupled plasma-atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammogram (CV) and charge–discharge studies. All the samples sintered at different temperatures have a typical layered structure with space group R3-m and good electrochemical performances. The sintering temperature has a remarkable effect on the electrochemical performance of the samples. The sample sintered at 730 °C shows the largest initial discharge capacity 191.1 mAh g⁻¹ (50 mA g⁻¹, 3.0–4.3 V) and the best cycling performance. The initial discharge capacity rises to above 200 mAh g⁻¹ with the voltage range 3.0–4.5 V.