Ferroelectric relaxor behaviour in Pb(Fe0.5Ta0.5)O3

The relaxor ferroelectric lead iron tantalate, Pb(Fe_0.5Ta_0.5)O₃ (PFT) is synthesized by Coulombite precursor method. The X-ray diffraction pattern of the sample at room temperature shows a cubic phase. The field dependence of dielectric response is measured in a frequency range 0.1 kHz — 1 MHz and in a temperature range from 173–373 K. The temperature dependence of permittivity (ɛ′) shows broad maxima at various frequencies. The frequency dependence of the permittivity maximum temperature (T _m ) has been modelled using Vogel-Fulcher relation.      

Effects of interaction of nanoparticles in a highly anisotropic ferrimagnet

This paper reports on a study of the field and temperature dependences of the parameters of the particle magnetic interaction in a densely packed system of nanocrystals of the highly anisotropic hexagonal ferrite BaFe₁₂O₁₉ with the particles distributed in diameter within the range 10—100 nm and having volumes satisfying the criterion of “small Stoner—Wohlfarth particles.” It is shown that the resultant particle interaction in the temperature range 300 K≤T≤640 K has a negative sign, whereas for T>640 K, it is positive. The maximum values of the parameter Δm allow classification of the interaction as moderate in strength. The temperature dependences of the interaction parameters are found to correlate with manifestation of the size and surface effects in the system, which are characteristic of small particles (transition to the superparamagnetic state, “surface” anisotropy, and reduced exchange interaction in a structurally defective near-surface layer of particles).     

The relation betweenT c and anharmonicity in Sn-base A15 superconductors

The absolute value of the recoil-free fraction was measured accurately at three reference temperatures in the range 300 K down to 4 K, in two Sn-baseA 15 superconductors with disparate superconducting properties. The higher-T _c compound Nb₃Sn (T _c≈18K) exhibits low-temperature anharmonicity; this is in contrast to the lattice-dynamics of the low-T _c isomorph V₃Sn (T _c≈4K) in which it is observed that harmonic binding of the Sn atoms is prevalent down to low temperatures. The difference in the superconducting properties of the two compounds is shown to correlate with the considerable difference in their lattice-dynamics.     

Analysis of the temperature dependence of the heat capacity of solid tin in the vicinity of its melting temperature

Summary The experimental temperature dependence of the heat capacityC _p(T) of solid tin (Sn) in its premelting region 402.07–502.22 K was investigated and two regions with different temperature dependences ofC _p(T) were found. In the far (from the melting temperatureT _m) region 402.07–485.88 K the experimentalC _p(T) of Sn is described by the standard vacancy model. In the close region 485.88–502.22 K it is described by the formation of complicated volumetric defects in the crystalline lattice of solid Sn near itsT _m.     

Cluster Structure of Liquid Alcohols,Water, and <Emphasis Type="Italic">n</Emphasis>-Hexane

The processes of cluster formation in liquid alcohols, water, methanol, n-hexanol, and n-hexane have been investigated by the method of flicker-noise spectroscopy. Two types of clusters — clusters with a close-packed structure and clusters with a loose structure — have been detected. The energy of formation of different clusters in methanol and n-hexane ranges, respectively, from −250 to +250 J/mole and from −50 to +50 J/mole. The smallest clusters of methanol, n-hexanol, water, and n-hexane consist, respectively, of six, two, eleven, and two molecules, and their largest clusters represent oscillators consisting, respectively, of 50,400, 17,200, 93,500, and 33,150 molecules at 274 K. In methanol at 271 K, more than 44 types of clusters consisting of 6, 97, 152, 219, 297, 492, 1029, 1368, 1560, etc. molecules were detected. In n-hexanol at 273 K, 57 types of clusters were detected. Models of small clusters are proposed. In water, the content of close-packed clusters is maximum at 277 K. The energy of formation/decomposition of small clusters in water ranges from −0.4 to +0.4 kJ/mole and increases with increase in the water temperature. The hysteresis of transformation of the (H₂O)₂₈₀ cluster in the process of heating and cooling of water in the temperature range 273–280 K was detected. Series of energy spectra of clusters in liquids at different temperatures are presented and discussed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 305–312, May–June, 2005.     

Magnetic susceptibility and characteristic features of the electronic structure of quasicrystalline alloys

Experiments are performed to determine the magnetic susceptibility of the icosahedral phase itself in the alloy Al₆₂Cu_25.5Fe_12.5 in the temperature range 3.9–1100 K. A new regularity is observed — the curves of the temperature dependences of the susceptibility and electrical conductivity are congruent. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 206–210 (10 February 1999)     

Hall effect and negative magnetoresistance in thin crystals of NbSe<Subscript>3</Subscript>

We have measured the Hall effect and the transverse magnetoresistance in NbSe₃ single crystals. In the liquid helium temperature range we observed an absolute negative magnetoresistance (NMR) — the value of the resistance under magnetic field being much lower than that at zero field — in NbSe₃ single crystals with a thickness less than 5 μm with the magnetic field oriented in the (b, c) plane. We show that this NMR effect is observed in the magnetic field range in which the Hall constant changes its sign. The results are qualitatively explained by the change of the surface scattering contribution to the magnetoconductance in the magnetic field range near the Hall voltage zero crossing.     

119Sn and151Eu Mössbauer study of EuBa2(Cu1-xSnx)3O7-y perovskites

Eu and Sn Mössbauer spectroscopy was used to study EuBa₂(Cu_1-xSn_x)₃O_7-y metallic oxides. The spectra are characteristic for Eu^III and Sn^IV states in all cases. The existence of at least two different Sn states was determined by decomposition of the Sn Mössbauer spectra. These Sn sites can be associated with nonequivalent Cu sites replaced by Sn atoms in the perovskite type lattice. Anomalous changes were observed in the isomer shifts and area fractions in the spectra measured at room temperature and at 77 K. It can be interpreted assuming low temperature phase transformation and phonon softening. Time dependent changes were found in the Sn spectra recorded at 77 K in the case of highest Sn concentration. The observed changes are consistent with a transitional stage of the low temperature phase transformation.     

Preparation of sol-gel method P2O5-Al2O3-SiO2 glasses and their characterization

Nanostructures P₂O₅-Al₂O₃-SiO₂ glasses were prepared by sol-gel method. The glasses were characterized by XRD, FTIR and TG/DTA methods. The average pore size of the glass was less than 3 nm as measured by N₂ adsorption — desorption method. The thermal stability was measured as a function of decomposition temperature and weight loss calculations. Proton conductivities of all samples increased with an increase in relative humidity (40–90 %), indicating that continuous paths suitable for proton conduction were developed when glasses heat treated at 300 °C due to the adsorption of water. The temperature dependence of the conductivity for all compositions increases with increasing temperature in the range 30–90 °C with relative humidity 70 %. The overall conductivity was in the range 10⁻⁴–10⁻³ S/cm for compositions.     

Elasticity of a cryo-insulation polymer foam coating in the temperature range 8–293 K

An apparatus is developed for investigating the dynamic deformation properties of cryoinsulation coatings in the temperature range 8–293 K. One type of cryo-insulation material — polyurethane foam — is chosen as the object of investigation. Test measurements on a polyurethane foam “pack” (metal substrate with a polyurethane foam coating) are performed at 0.01 Hz in the temperature range 8–293 K. A jump in the temperature dependence of the dynamic shear modulus (by two orders of magnitude) is observed in the temperature range 54–63 K. This feature is attributed to the solidification of the air present in the pores of the polyurethane foam. Such a transition results in cementation of the polyurethane skeleton of the coating by the nitrogen and oxygen “ice” that is formed. Zh. Tekh. Fiz. 69, 116–118 (February 1999)     

Electron mobility in compensated VPE GaAs films

Electron Hall mobilities were measured on a series of intentionally compensated vapor phase epitaxy (VPE) GaAs layers. Using Sn and Zn as dopants, compensation ratiosK=(N_D+N_A)/(N_D-N_A) as high as 50 were obtained. Already for samples with the lowestK values the 300 K mobilities are higher than the 77 K values. In the range 20<T<100 [K] the data may be represented by μ∼T ^α with α increasing from 0.6 to 1.1 with compensation. The experimental μ values are smaller than those predicted from current models in all cases. It appears that scattering at ionized impurities is the dominant process also at temperatures well above 77 K, and that this scattering process is quantitatively underestimated in current models.     

Electronic and ionic conductivity in CaTiO3

The present work describes the electrical conductivity of undoped CaTiO₃ in terms of the electrical conductivity components corresponding to electrons, electron holes and ionic charge carriers in the temperature range 973 K — 1323 K and under controlled oxygen partial pressure (10 Pa — 72 kPa). These data are considered in terms of the transference numbers of the respective charge carriers. It appears that the ionic conductivity component assumes maximum at the n-p transition when the ionic transfer number reaches 50% of the total conductivity value at 1323 K. The present study also includes the determination of the activation energy of the conductivity component related to ions (162.1 kJ/mol), electrons (134.2 kJ/mol) and electron holes (86.2 kJ/mol). The data obtained in this work indicate that undoped CaTiO₃ exhibits a substantial level of ionic conduction that cannot be ignored in a quantitative analysis of electrical conductivity data.     

金属间化合物PrMn6Sn6的结构、磁性与119Sn穆斯堡尔谱研究

采用电弧熔炼法制备了金属间化合物PrMn₆Sn₆.X射线衍射表明该化合物具有HoFe₆Sn₆型(空间群为Immm)晶体结构.磁测量表明该化合物为铁磁性，居里温度为325　K.在15—360　K范围内测量了¹¹⁹Sn穆斯堡尔谱，得到了8个Sn原子晶位的转移超精细场随温度的变化，并且讨论了Mn亚晶格与Pr亚晶格的磁有序方向. 关键词： 6Sn₆')" href="#">PrMn₆Sn₆ 穆斯堡尔谱 磁结构     

Large magnetocaloric effect and magnetoresistance behavior in Gd4Co3

We report a large entropy change (ΔS) below 300 K, peaking near T _C = 220 K, due to isothermal change of magnetic field, for Gd₄Co₃, with a refrigeration capacity higher than that for, say, LaFe_11.4Si_1.6, ordering magnetically in the same temperature range. A noteworthy finding is that the isothermal magnetization is nonhysteretic — an important criterion for magnetic refrigeration without loss. ΔS behavior is also compared with that of magnetoresistance.     

Frequency response analysis of ionically conducting mixed system (1-x)CuI - xAg2MoO4 (0.15 ≤ x ≤ 0.55)

A systematic analysis of the electrical response of the mixed system (1-x)CuI — xAg₂MoO₄ (0.15≤x≤0.55) over the temperature range 297 – 447 K in the 20 Hz — 1 MHz frequency domain has been reported. Relaxation processes associated with individual compositions of this heterogeneous mixture of polycrystalline samples have been identified through a combined analysis of modulus and impedance spectral formalisms. The detailed analysis of these relaxation processes has indicated that AgI and Ag₂MoO₄ phases are the predominant sources of electric conduction in the case of samples in the composition region 0.33≤x≤0.55 whereas in those samples having x<0.33, the presence of Cu₂MoO₄ phase in the mixture is found to make a definite contribution to their effective electric conduction.     

D.C. conductivity of transparent conductive ZnO:Al films in the temperature range 80–360 K

An experimental study of the temperature dependence of the d.c. conductivity σ as a function of temperature T in the range from 80–360 K on nanocrystalline ZnO:Al films (Al³⁺ 2%) of thickness 500 nm prepared on glass microscope slides by a dip — coating method is presented. The electrical conductivity σ, which at room temperature varied between 0.1 to 2.7 S/cm, increased almost linearly with T for all the samples. Measurements of the Hall coefficient at room temperature and in a magnetic field of 1.2 T, gave R_H=0.53 cm³C⁻¹, from which a carrier concentration of n=1.18×10¹⁹ cm⁻³ and a carrier mobility of μ=1.40 cm²/Vs were deduced. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.     

Lattice vibrational behavior of XSn4 (X=Au,Pd, Pt) compounds

Temperature dependent¹¹⁹Sn Mössbauer effect measurements on AuSn₄, PdSn₄, and PtSn₄ compounds in the temperature range of 10 to 295 K shows the presence of a Sn⁴⁺ site. Variation of thermal shift and the Debye-Waller factor shows that the mean-squared displacement (lnf) and mean-squared velocity (δ) of the tin nuclei are both characterized by a Debye temperature of 238, 255, and 304 K in AuSn₄, PdSn₄, and PtSn₄, respectively. No discernible evidence of a phonon mediated structural transition is observed in the temperature range studied.     

μ + Knight shift and spin relaxation in indium single crystalKnight shift and spin relaxation in indium single crystal

μ ⁺ SR measurements have been performed in a single crystal indium sample between 12 K and 300 K with a stroboscopic μSR spectrometer. The muonic Knight shiftK _μ and the muonic depolarization rate σ were obtained for various angles θ between the tetragonal crystallinec-axis and the direction of the external field. The isotropic part ofK _μ is only weakly temperature dependent and is consistent with the estimated Pauli spin susceptibility value. At a temperature of 12 K the angular dependence ofM ₂ (the second moment of the field distribution at the muon, obtained from the measured σ(θ) values) allows a clear determination of the muon location — the symmetric tetrahedral site. The observed anisotropicK _μ cannot be explained by the dipoles at the In atoms responsible for the bulk magnetic susceptibility but probably originates from an anisotropic Pauli spin susceptibility.     

The study of optical properties of amorphous thin films of mixed oxides In<Subscript>2</Subscript>O<Subscript>3</Subscript>—SnO<Subscript>2</Subscript> system,deposited by co-evaporation

A discussion of optical properties of mixed oxides In₂O₃—SnO₂ system is presented. Film thickness, substrate temperature, composition (in molar %) and annealing have a profound effect on the structure and optical properties of these films. Initially the increase in band gap with the increase of SnO₂ content in In₂O₃ is due to the increase in carrier density as a result of donor electrons from tin. The decrease in band gap above the critical Sn content is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The increase in band gap with film thickness is caused by the increase in free carrier density which is generated by (i) Sn atom substitution of In atom, giving out one extra electron and (ii) oxygen vacancy acting as two electrons donor. The decrease in band gap with substrate temperature and annealing is due either to the severe deficiency of oxygen, which deteriorate the film properties and reduce the mobility of the carriers, or to the formation of indium species of lower oxidation state (In²⁺).     

Structural and magnetic properties of RET2Sn2 compounds (RE=La,Ce, Sm; T=Ni,Cu)

The following compounds have been synthesized: LaCu₂Sn₂, CeCu₂Sn₂, SmCu₂Sn₂ and SmNi₂Sn₂. By means of X-ray diffraction their structure was determined to be primitive tetragonal of CaBe₂Ge₂-type (space group P4/nmm) and the lattice parameters were obtained.¹¹⁹Sn Mössbauer measurements were performed in a temperature range between 4.2 K and 300 K. The temperature dependence of the Lamb-Mössbauer factor reveals considerable softening of lattice vibration modes below 160 K. Only SmCu₂Sn₂ orders magnetically above 4.2 K.