Preparation and dielectric properties of Si3N4 thin films

Thin Si₃N₄ films of thickness 50–1500 nm were prepared by a low pressure, room temperature chemical vapour deposition process. The dielectric properties of the layers were studied in the frequency range from 10 Hz to 1 MHz and at temperatures between 77 and 400 K. We observed a σ'(ω, T) = A(T)ω^s(T) dependence with s?1 (where σ' is the real part of the a.c. conductivity). For samples prepared in various ways, A varied between a constant value and a superlinear dependence on temperature. At 77 K, however, σ' for all the samples was found to be approximately the same (about 8 × 10^?12 Ω^?1 cm^?1 at 1 kHz) irrespective of the preparation parameters.     

Thermal conductivity of single and multi-stacked DI-BSCCO tapes

We have measured the temperature dependence of the thermal conductivity, κ(T), for DI-BSCCO^® tapes fabricated by Sumitomo Electric Industries, Ltd., which are (Bi,Pb)₂Sr₂Ca₂Cu₃O_8+x tapes sheathed with Ag or Ag-Au alloy. The κ(T) of the tape sheathed with Ag (residual resistance ratio (RRR) = 15) decreases with decreasing temperature and starts to increase rapidly below 60 K, with a maximum at around 15 K. On the other hand, the κ(T) of the tape sheathed with Ag-5.4 wt%Au alloy has a very low value that decreases monotonically with decreasing temperature. At around 77 K, the absolute values of κ(T) for both tapes were about and , respectively. The κ(T) of a stacked sample, in which six DI-BSCCO tapes sheathed with Ag are soldered, was also measured. The measured κ(T) was fairly well reproduced by the estimated κ(T), which was calculated using the measured κ(T) of the single tape and solder.     

Heat capacity and electrophysical properties of GdMeFe2O5(Me — Li, Na, K, Cs)-type ferrites

The heat capacity of GdMeFe₂O₅(Me — Li, Na, K, Cs) is investigated within the temperature range of 298.15–673 K by a calorimetric method. λ-points are revealed in the C _p ^○ (T) curves at 448 K and 598 K in GdLiFe₂O₅, at 473 K and 573 K in GdNaFe₂O₅, at 448 K and 598 K in GdKFe₂O₅, and at 448 in GdCsFe₂O₅ related to a phase transition of the second kind. The temperature dependencies are calculated for the thermodynamic functions C _p ^○ (T), H ^○(T)-H ^○(298.15), S ^○(T), and Φ**(T). The electrophysical characteristics of the synthesized ferrites are studied within the temperature range of 303–493 K: Effects similar to those found in the C _p ^○ (T) curves are also revealed in the log?(T) and logR (T) curves. The compositions are shown to exhibit a semiconductor-type electrical conductivity. At the T _cond points of the ferrites, the semiconductor-type conductivity changes the metal type one and both the capacities and permittivities vary sharply, and that may be related to a ferroelectric phase transition (the Curie and the Neel points). These effects provide a certain possibility to clarify the nature of the λ-points in the C _p ^○ (T) curves.     

New Magnetic Phase Transitions in the Tetragonal Compounds PrBa2Cu3O6+x at Low Temperature

The anomalous magnetic properties of Pr ions in the PrBa₂Cu₃O_6+x system are investigated at low temperature. Measurements of the specific heat C _P(T) and the magnetic susceptibility χ(T) are performed on ceramic samples in the tetragonal structure with x=0.44 and x=0. Two new magnetic transitions are observed below the Néel temperature of the Pr antiferromagnetic ordering $T_{\mathrm{N}}^{\mathrm{Pr}} \sim 9\mbox{--}10~\mathrm{K}$ . The first one is observed at the low-critical temperature T _cr～4–5?K and the second one is observed at $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}} \sim 6\mbox{--}7~\mathrm{K}$ , respectively. Assuming that ΔC _P(T) can be used to represent the Pr contribution to the specific heat C _P(T), the data are well fitted for T<T _cr by using the development of ΔC _P(T)/T=ΔA(T ²)^?3/2 +Δγ+M(T ²) ¹ +m(T ²) ² . The values of the electronic coefficient Δγ are found much lower than all previous results obtained in compounds of the orthorhombic structure, and this is, in good agreement with the insulating character of our non-superconducting samples. The high values obtained for the coefficient M, permits us to confirm the existence of strong Pr–Pr exchange interactions. Some non-linear effects attributed to the values of the coefficient m are revealed and discussed in terms of the previous Pr–Cu coupling with a spin reorientation phase transition of both spin sublattices around $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}}$ . The appearance of a weak ferromagnetic tendency in the magnetic susceptibility analysis below T _cr, could be associated with the reordering of the Pr subsystem.     

Cesium dizirconium phosphate: Synthesis and thermal properties

Crystalline CsZr₂(PO₄)₃ with the NZP [NaZr₂(PO₄)₃] structure was prepared by a sol gel procedure. The purity and composition of the sample were determined by scanning electron microscopy with energy-dispersive X-ray analysis as well as by X-ray phase analysis and IR spectroscopy. CsZr₂(PO₄)₃ is thermally stable in the range 7 K < T < 1553 K. Temperature dependences of the heat capacity C _p ⁰ = f(T) and thermal conductivity λ = f(T) of the phosphate in the range 320–650 K corresponding to thermal conditions of a nuclear waste repository were studied. The standard thermodynamic functions C _p ⁰ (T), H ⁰(T)–H ⁰(0), S ⁰(T), and G ⁰(T)–H ⁰(0) were calculated. The thermodynamic functions of formation of CsZr₂(PO₄)₃ were calculated. The possibility of decreasing the temperature of the synthesis-immobilization to 1000 K was experimentally confirmed.     

Scaling Analysis of Conductivity-Related Quantities of YBCO Using Ac Loss Peak Temperature as Scaling Parameter

The ac response of polycrystalline YBCO sample in the frequency range 10–2500 kHz has been measured by using a contactless method. For this purpose, two parameters S(ω,T) and S′(ω,T) have been derived from the measured impedance of the system. The parameters S(ω,T) and S′(ω,T) are related to the real and imaginary parts of ac conductivity, respectively. Both the real and the imaginary parts of ac conductivity show frequency-dependent nature. All the observed features have been interpreted by considering the flux flow losses. Due to the flux penetration, S(ω,T) exhibits a peak below the transition temperature (T _C ), which could be explained on the basis of Anderson’s thermally activated flux creep model. Finally, we have applied a model-independent scaling technique to scale all the measured data and obtained the scaling functions by curve fitting method. The same scaling analysis has been found to be also useful for ac susceptibility data.     

The Effects of Mn Substitution on Magnetization Reversal Properties in Gd0.7Ca0.3MnO3

Low temperature magnetization in polycrystalline Gd_0.7Ca_0.3Mn_1?x M _x O₃ (M=Cr, Ga, Ru; x=0, 0.2) has been investigated. The samples were prepared via the conventional solid state reaction method. For all the samples, the paramagnetic to ferrimagnetic (PM-FiM) transition temperature (say T _max) can be well defined from the temperature dependent ac susceptibility data. The negative magnetization suppresses due to 20 % Cr or Ga doping at the Mn site. On the other hand, below the compensation temperature (T _comp), the nature of the Ru doping sample is almost similar to that of undoped Gd_0.7Ca_0.3MnO₃. The nonmagnetic Ga doping drastically reduces magnetization and T _max shifts to a lower temperature. However, Ru and Cr doping increase the value of T _max. The network of canted Mn³⁺/Mn⁴⁺ moments changes with the substitution of Cr, Ga, and Ru at the Mn site giving rise to the variation of the internal magnetic moment. Thus, the antiparallel coupling of the Gd moments with Mn/M changes and affects the low temperature magnetization reversal properties.     

Terahertz Conductivity of Overdoped Y1−x Ca x B2Cu3O7−δ

In the current work we have investigated the terahertz response of Ca overdoped YBaCuO thin films using both time and frequency domain spectroscopy methods. For both methods a basic data analysis was performed using the two fluid and a variable dielectric function (VDF) models. The imaginary part of the conductivity was proportional to 1/ω, known from the delta-function response. The real part of conductivity showed a well known frequency and temperature dependence, where it increases below T _c and obtains maxima at about 50 K. However, a sharp decrease of the real part of the conductivity was observed at about 10 cm^?1. This decrease occurs below T _c and becomes dominant as temperature decreases. It was observed on the 5% and 10% Ca doped samples but it was more dominant on the 10% case. Moreover, this sharp decrease in σ ₂(ω)at 10 cm^?1 was not observed in optimally doped YBCO samples. We would like to stress at this point that these values are much smaller than those obtained by Microwave and Tunneling measurements, arguing for the existence of a complex order parameter in the overdoped regime with an imaginary component of about 1.8 meV.     

Heat Capacity and thermodynamic functions of DyMe<Superscript>II</Superscript>Cr<Subscript>2</Subscript>O<Subscript>5.5</Subscript>(Me<Superscript>II</Superscript>-Mg,Ca) in the range from 298.15 to 673 K

The calorimetric method is used to investigate the heat capacity of DyMe^IICr₂O_5.5(Me^II-Mg, Ca) chromites in the range from 298.15 to 673 K. The C _p ⁰ ～ f(T) curves exhibit λ-like effects at 348 and 548 K for DyMgCr₂O_5.5 and at 473 K for DyCaCr₂O_5.5, which apparently relate to second-order phase transitions. The temperature dependences are calculated for thermodynamic functions C _p ⁰ (T), H ⁰(T)-H ⁰(298.15), S ⁰(T), and Φ**(T).     

Tables of the Inverse Laplace Transform of the Function [... formula ...]

The inverse transform, g(t) = ?^?1(e^?sβ), 0 < β < 1, is a stable law that arises in a number of different applications in chemical physics, polymer physics, solid-state physics, and applied mathematics. Because of its important applications, a number of investigators have suggested approximations to g(t). However, there have so far been no accurately calculated values available for checking or other purposes. We present here tables, accurate to six figures, of g(t) for a number of values of β between 0.25 and 0.999. In addition, since g(t), regarded as a function of β, is uni-modal with a peak occurring at t = t_max we both tabulate and graph t_max and 1/g(t_max) as a function of β, as well as giving polynomial approximations to 1/g(t_max).     

The variation of thermoelastic properties under conditions of variation of isotopic composition of diamond

The parameters of interatomic interaction in diamonds of ¹²C and ¹³C isotopes are determined. The parameters are determined by two methods, namely, from the elastic modulus (potential no. 1) and from the sublimation energy at T = 0 K (potential no. 2). Based on these parameters, the Debye model is used to calculate the isobaric temperature dependences of the thermoelastic properties for isotopically different diamonds, namely, the coefficient of thermal expansion (CTE), the density, the elastic modulus B _T , and the specific heat capacity. It is demonstrated that the best agreement with the experimentally obtained dependences of the foregoing parameters is obtained when potential no. 1 is used in calculations. The values of CTE, density, and heat capacity increase in the case of transition from ¹²C diamond to ¹³C diamond. It is demonstrated that the inequality B _T (¹²C) < B _T (¹³C) is valid at T = 0 K, which is associated with the reduction of interatomic spacing in the case of transition from ¹²C diamond to ¹³C diamond. However, as the temperature increases, the volumetric isotopic effect in diamond decreases. It is found that the B _T (T) dependences for ¹²C and ¹³C diamonds intersect at a temperature below the Debye temperature. Therefore, at high temperatures, the elastic modulus for light-isotope diamond comes to exceed that for heavy-isotope diamond, B _T (¹²C) > B _T (¹³C). Experimental results are given which confirm this effect. The variation of the properties of isotopically different diamonds with increasing pressure is discussed.     

Thermodynamic properties of (TeO2) n (WO3)1 − n glasses in the range 0–650 K

The heat capacity of (TeO₂) _n (WO₃)_{1 ? n} tellurite glasses with n = 0.75, 0.78, 0.85, and 0.90 has been determined using precision adiabatic calorimetry (6–350 K) and dynamic scanning calorimetry (320–650 K), and the thermodynamic characteristics of their glassy state and devitrification have been evaluated. The experimental heat capacity data have been used to calculate the standard thermodynamic functions of the glassy and supercooled liquid states at temperatures from T → 0 to 650 K: heat capacity C _p ⁰ (T), enthalpy H ⁰(T) — H ⁰(0), entropy S ⁰(T), and Gibbs function G ⁰(T) — H ⁰(0). The character of structural heterodynamicity of the tellurite glasses has been assessed by processing the low-temperature heat capacity data using the multifractal formulation of the Debye theory of heat capacity of solids. The composition dependences of the devitrification temperature and 298.15-K thermodynamic functions have been obtained, and the 298.15-K C _p ⁰ of tellurium dioxide has been estimated. The thermal and thermodynamic properties of the (TeO₂) _n (WO₃)_{1 ? n} tellurite glasses have been compared with those of (TeO₂) _n (ZnO)_{1 ? n} glasses.     

Thermodynamic properties of TeO2-ZnO glasses in the range 0–650 K

The heat capacity C _p ⁰ of (TeO₂)_n(ZnO)_{1 ? n} (n = 0.65, 0.70, 0.80) tellurite glasses has been determined by precision adiabatic (6–350 K) and dynamic scanning (320–650 K) calorimetry. The thermodynamic characteristics of their devitrification and glassy state have been determined. The experimental data have been used to calculate the standard thermodynamic functions of samples in the glassy and “supercooled liquid” states (0–650 K): heat capacity C _p ⁰ (T), enthalpy H ⁰(T) ? H ⁰(0), entropy S ⁰(T) ? S ⁰(0), and Gibbs function G ⁰(T) ? H ⁰(0). Multifractal processing of the low-temperature heat capacity data has been used to assess the character of structural heterodynamicity of the tellurite glasses. The heat capacity of the glasses has been analyzed in comparison with that of their constituent oxides. The composition dependences of the glass transition temperature, crystallization onset temperature, and thermodynamic functions at 298.15 and 600 K have been obtained.     

Superconductivity of Bi Confined in an Opal Host

Superconductivity is observed in a composite of rhombohedral crystalline bismuth nanoparticles imbedded in an insulating porous opal host via electrical transport and AC magnetic susceptibility. The onset of superconductivity in this system occurs in two steps, with upper transition temperature T _c,U =4.1 K and lower transition temperature of T _c,L =0.7 K, which we attribute to the granular nature of the composite. The transition at T _c,U is observed to split into two transitions with the application of a magnetic field, and these have upper critical fields extrapolated to T=0 K of H _c2,1(0)=0.7 T and H _c2,2(0)=1.0 T, corresponding to coherence lengths of ξ ₁(0)=21 nm and ξ ₂(0)=18 nm, respectively. We suggest that because of the lack of bulk-like states in the Bi nanoparticles due to confinement effects, superconductivity originates from surface states arising from Rashba spin-orbit scattering at the interface.     

Thermodynamic and electrophysical properties of LaSrMnFeO5.5 ferrite

The isobaric heat capacity of LaSrMnFeO_5.5 ferrite is investigated within the temperature range of 298.15?C673 K by a calorimetric method. On the curve of the dependence of the heat capacity on temperature, the ??-type effect is revealed relating to a phase transition of the second kind. Temperature dependencies of the thermodynamic functions S ⁰(T), H ⁰(T) -H ⁰(298.15), and ?? ^xx (T) are calculated. The temperature dependencies of permittivity and electrical resistance are studied within the temperature range of 303?C493 K, and the results show that the composition under study has semiconductor properties.     

Study of the Magneto-Resistivity and Dependence of Percolation in La0.75Ca0.1Sr0.15Mn1−x Ga x O3 Compounds

We present a study of the effect of Ga-doping on the physical properties of La_0.75Ca_0.1Sr_0.15Mn_1?x Ga _x O₃ (x=0.025, 0.075 and 0.1) compounds prepared by the sol-gel method. The variation of the magnetization (M) vs. temperature (T), under an applied magnetic field of 0.05 T, reveals a ferromagnetic–paramagnetic transition for all samples. The magnetization behavior and the Curie temperature T _C have shown a large dependence on the fractional composition x. In fact, the M(T) curves have revealed the presence of a long-range ferromagnetic state below T _C. The magnetotransport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements. We have noted that these samples present an electrical transition from a paramagnetic-semiconductor state to a ferromagnetic-metallic one, when decreasing temperature. We have used the phenomenological equation for conductivity under a percolation approach, which is based upon an approach that the system consists of the phase separated ferromagnetic metallic and paramagnetic insulating regions. We have then fitted the resistivity data measured in the range of 15–300 K and found that the activation barrier decreases with the raising Ga³⁺ ion concentration.     

Electrical and Thermal Transport Properties of Transition Metal Substituted in Electron-Doped La0.9Te0.1Mn1?x M x O3 Compounds (M=Cr and Al)

Systematical studies of resistivity ??(T), thermopower S(T), and thermal conduction ??(T) have been performed on the electron-doped manganites La_0.9Te_0.1Mn_1?x Cr(Al) _x O₃ (0.05??x??0.20). The Cr005 and Al005 samples exhibit an insulator-metal transition in the ??(T) curves, however, other samples present insulating behaviors in the whole measured temperature. The S(T) data increases with decreasing temperature and develop a peak at $T_{S}^{P}$ for all samples, with decreasing temperature further, another characteristic temperature $T_{s}^{m}$ is observed. The fits of ??(T) and S(T) data in the high temperature region are presented, and the result shows that the electron conduction is governed by the VRH mechanism for Al-doped samples and the SPC mechanism for Cr-doped ones. As to thermal conduction ??(T), it is suggested that it comes from two sides, one is the phonon-phonon scattering due to disorder and the other is the spin-phonon interaction.     

Effect of He addition on the heating characteristics of substrate surface irradiated by Ar thermal plasma jet

Effect of He addition to Ar as the discharge gas on the substrate surface temperature during thermal plasma jet (TPJ) annealing is investigated. The maximum surface temperature (T_max) increases from 1370 to 1470 K with increasing He fraction (R_He) from 0 to 28%, then decreases to 1040 K with increasing R_He to 86%. It has been confirmed that the TPJ is efficiently concentrated when He addition is around 30%, which suggests that the increase in T_max is due to the increase in the power density induced by thermal pinch effect. By adding 30% He and increasing the total gas flow rate to 15.4 L/min, T_max is increased to 1580 K.     

Compositional effects on the optical and thermal properties of potassium aluminophosphate glasses

The K₂O–Al₂O₃–P₂O₅ glass system has been examined and various compositions have been melted. Their optical and thermal properties have been measured to assess their potential for athermalisation. The addition of alumina (Al₂O₃) increases the refractive index (n) and glass transition temperature (T_g) and decreases the thermal expansion coefficient (α), consequently leading to positive thermo-optic coefficient (dn/dT). In addition to thermal expansion, polarisability of the glass also affects dn/dT. Generally, glasses must exhibit negative dn/dT to counter thermal expansion, in order to have potential application in athermalisation.     

Evidence of Phase Separation in the P-T Phase Diagram of the La0.75Ca0.25MnO3 Manganite by Infrared Measurements

Recent infrared absorption measurements performed at different pressures and temperatures on the La_0.75Ca_0.25MnO₃ manganite provided an estimate of the insulator-to-metal transition temperature T _IM(P), i.e., the P-T phase diagram of a pseudocubic manganite. Here we consider in detail the P- and T-dependence of the absorption spectral weights n ^*. The n ^*(T,P) behavior gives evidence of phase-separation between conducting and insulating domains in the P-T phase diagram, and allows to establish the occurrence of a characteristic temperature T ^* ? 0.6 T _IM. For T > T ^*, when insulating domains decrease on decreasing temperature or on increasing pressure, it is possible to distinguish a metallic region (connected metallic domains) for T ^* < T < T _IM, and an insulating region (disconnected metallic domains) for T > T _IM. Below T ^*, no reduction of the insulating domains, that may still exist, occurs.