Electrical resistivity and thermal conductivity of UP1−xSx

UP, US, and their solid solutions of several compositions were prepared, and the electrical resistivities of these samples were measured from liquid nitrogen temperature to 1000 K and the thermal diffusivities from 300 to 1000 K. It was shown that the resistivity of UP_1?xS_x at the paramagnetic region arose mainly from the scattering of conduction electrons by disordered spins localized at uranium ion sites. The resistivity of UP_0.4S_0.6 showed another anomaly below the transition temperature. A gentle hump of the thermal diffusivity of UP was observed at about 650 K. This was concluded to be due to the anomalous negative temperature coefficient of electrical resistivity observed above the Néel temperature up to about 550 K. The composition dependence of thermal conductivity of UP_1?xS_x was compared with that of UC_1?xN_x by separating the total conductivity into electronic and phonon contributions.     

Electrical conduction of a quasi-one dimensional Nb3S4 single crystal

With respect to single crystals of Nb₃S₄ the electrical resistivity from 2.8 K to 300 K and the magnetoresistance at 4.2 K were measured. The resistivity is represented as a sum of a temperature independent and an intrinsic temperature dependent component. The temperature dependence of the intrinsic resistivity subjects to T₃ form between 7 and 50 K above which it becomes weaker than T₃ approaching a T linear from. This behaviour is discussed in terms of the electron-electron Umklapp scattering. The ratio of the resistivities perpendicular and parallel to the c-axis takes about 15 between room temperature and 50 K. The transverse magnetoresistance is proportional to the magnetic field. The longitudinal magnetoresistance is too small to be measured.     

Electrical resistivities of the intermetallic compounds NpRu2 and NpOs2

The electrical resistivities of the cubic intermetallic compounds NpRu₂ and NpOs₂ have been measured in the temperature range 1.5–300° K. The resistivity of NpRu₂ varies as T² up to 13° K. This behavior is in agreement with the predictions of the localized-spin-fluctuation model. The resistivity-temperature curve of NpOs₂ has the characteristics of a material that orders magnetically. The ordering temperature T_C = (7.4±0.5)°K was obtained from analysis of the data. The difference between the magnetic properties of NpRu₂ and NpOs₂ is discussed in terms of the variation in the actinide-actinide interatomic distance in these compounds.     

Self-diffusion of uranium in uranium dicarbide UC2

The self-diffusion of uranium in uranium dicarbide, UC₂, was measured between 1670 and 2500 K using the α-energy degradation method with the thin layer condition and U-233 as tracer. The activation enthalpy was 5.7 ± 0.2 eV. A discontinuity was indicated at ≈ 2050 K, the transition temperature of α-UC₂ to β-UC₂.     

Increased cubic–tetragonal phase transition temperature and resistivity hysteresis of surface vacuum annealed SrTiO3

Electrical properties of SrTiO₃ single crystal samples treated by an anisotropic surface annealing technique under reducing conditions have been investigated in the temperature range of 35 K–300 K. Optical and atomic force microscopy show that annealing gives rise to polycrystallization and the formation of colored dendritic structures. Carrier concentrations and mobilities determined by Hall measurements as well as resistivities detected by van der Pauw measurements show the expected metallic behavior due to oxygen vacancy doping. Moreover, the temperature dependent resistivities indicate a cubic-to-tetragonal phase transition, which to our knowledge has not been reported before. Additionally, the transition occurred up to 53 K above the known bulk transition temperature T _C at 105 K with a hysteresis up to a temperature of 220 K. Both phenomena possibly arise from dislocations and associated strain fields introduced by surface annealing that are assumed to lower the free energy of the tetragonal phase and simultaneously pin tetragonal domains. Thus, microregions of the tetragonal phase persist above T _C causing the hysteresis in resistivity up to ∼12%. This effect possibly provides new chances for future oxide based non-volatile data-storage devices.     

Resistivity anisotropy and charge density wave in 2H - NbSe2 and 2H - TaSe2

The in-plane and out-of-plane resistivities of both 2H-TaSe₂ and 2H-NbSe₂ were determined down to 10 K. For both compounds, the resistivity anisotropy shows notably a slope change at temperatures where a CDW transition is expected to occur. On the other hand, for both compounds the resistivity anisotropy at the lowest temperature of measurement is much greater than expected by the Lawrence–Doniach model, which relates the critical magnetic field anisotropy to the normal state resistivity anisotropy for 3D-anisotropic superconductors.     

Thermal expansion and kinetic coefficients of crystals

Electrical (ρ) and thermal (W) resistivities and thermal expansion coefficient (β) of Cu, Zn, Al, Pb, Ni, β-brass, Al₂O₃, NaCl, Si, SiO₂(∥), and SiO₂(⊥) were simultaneously measured with standard four-probe, absolute steady-state, and quartz dilatometer techniques. Measurements of Ni and β-brass were performed at temperatures from 300 to 1100 K and measurements of all other samples were made between 90 and 500 K. This temperature range includes the range below and above the Debye temperature (T_D). The total uncertainties of the specific electrical and thermal resistivities and thermal expansion coefficient (TEC) measurements are 0.5%, 3.0%, and (1.5-4.0%), respectively. The universal linear relationship between the electrical and thermal resistivities and βΤ over the wide temperature range was found experimentally. Using the Landau criterion for convection development for ideal phonon and electron gases in the solids, the universal relations, ρ^ph/ρ^*≡βT and W^ph/W^*≡βT (where ρ^ph is the phonon electrical resistivity, is the characteristic electrical resistivity, W^ph is the phonon thermal resistivity, and W^*=k_BG/qc_p is the characteristic thermal resistivity) between relative phonon electrical and phonon thermal resistivities and βΤ were derived. The derived universal relations provide a new method for estimating the kinetic coefficients (electrical and thermal resistivities) from TEC measurements.     

Low temperature resistivities of FexNi80-xP14B6 metallic glasses

The resistivities of six Fe_xNi_80-xP₁₄B₆ alloys have been measured between 1.5 and 50 K. It is found that the resistivity variations both below and above the resistivity minima depend on the transition metal composition. The room temperature coefficients of the resistivity indicate the existence of the magnetic contribution to the resistivity.     

The electrical resistivity of some uranium tellurides

Electrical resistivity of U₃Tein4, U₂Te₃ (cubic) and UTe₃ has been measured over temperature range 4.2–300 K. The two former compounds appear to be semimetallic conductors while the last one has semiconducting character. The results are discussed in the terms of available magnetic data.     

Anomalous behavior in the low temperature properties of UPd3

The low temperature specific heat of the hexagonal intermetallic compound UPd₃ reveals a contribution from low lying crystal field levels. In annealed or single crystal samples, sharp phase transitions are observed at temperatures of 6 and 7 K respectively. Correlation with resistivity, susceptibility and X-ray measurements in this temperature range indicate that the collective phenomenon is probably due to the electric quadrupole interaction between the U⁴⁺ ions.     

Atomic-vacancy ordering and magnetic susceptibility of nonstoichiometric hafnium carbide

Experimental data on the magnetic susceptibility of nonstoichiometric hafnium carbide HfC_y(0.6< y<1.0) are presented. Anomalies are found in the temperature dependences of the magnetic susceptibility of the carbides HfC_0.71, HfC_0.78, and HfC_0.83 in the temperature range 870–930 K. These anomalies are due to the formation of a superstructural short-range order in their nonmetallic sublattice. It is shown that the short-range order in the carbides HfC_0.71 and HfC_0.78 corresponds to the ordered phase Hf₃C₂, while in the carbide HfC_0.83 it corresponds to the ordered phase Hf₆C₅. It is found that the magnetic susceptibility of the carbide HfC_0.78 in the temperature interval 910–980 K is zero. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 296–301 (25 February 1999)     

Magnetotransport parameters of La0.67Ca0.33MnO3 films grown on neodymium gallate substrates

Weakly mechanically stressed 40-nm-thick La_0.67Ca_0.33MnO₃ films have been grown coherently on a (001)NdGaO₃ substrate by laser evaporation. The electrical resistivity ρ of the La_0.67Ca_0.33MnO₃ film reaches a maximum at a temperature T _C ≈ 255 K. At temperatures below 0.6T _C, the temperature dependences of ρ are well approximated by the relation ρ = ρ_def + C ₁ T ² + C ₂ T ^4.5, in which the first term on the right-hand side accounts for the contribution of structural defects to electrical resistivity, and the second and third terms stand for those of the electron-electron and electron-magnon interactions, respectively. The parameters ρ_def ≈ 1 x 10^?4 Ω cm and C ₁ ≈ 7.7 × 10^?9 Ω cm K^?2 do not depend on temperature and magnetic field H. The coefficient C ₂ decreases with increasing H to reach about 4.9 × 10^?15 Ω cm K^?4.5 at μ₀ H = 14 T.     

The electronic properties of chromium borides

Measurements of magnetic susceptibility between 300 and 100°K and of resistivity between 300 and 4.2°K are reported for the five intermediate compounds Cr₂B, Cr₃B₃, CrB, Cr₃B₄ and CrB₂. With the exception of CrB₂ (antiferromagnetic T_N = 88°K) all the compounds were found to be weakly temperature dependent paramagnets. Large, orbital contributions to the susceptibility are proposed for Cr₂B and Cr₅B₃. It is suggested that with the formation of discrete boron networks and the associated change in band structure in the higher borides this contribution diminishes very rapidly. At low temperatures Cr₂B₁ CrB and CrB₂ were all found to have a prominent T² behaviour in ρ(T). At high temperatures the resistivities of CrB and CrB₂ were found to vary linearly with temperature, the resistivity of Cr₂B on the other hand seemed to follow a T(1 ? BT²) law.     

Mn的价态对La0.8Ba0.2MnO3电磁性能的影响

在2—390K温度之间研究了La_0.8Ba_0.2MnO₃的 磁矩、磁电阻与温度的关系.发 现以不同价态的Mn元素引入得到的La_0.8Ba_0．2MnO₃ ，性能虽然都存在金属 —绝缘体转变，以及在磁场作用下居里温度附近电阻率变化非常显著的特点，但是价态对磁 性转变温度T_C，金属—绝缘体转变温度T_mi，以及磁电阻极大 值温度T_MR的影 响都非常显著.三种价态相比较，使用二价Mn的电阻率最低以及磁性转变温度更接近室温.认 为影响材料性能的主要因素是材料制备时引进的Mn元素的价态，由于原料价态的不同而形成 的氧空位浓度变化，进而影响了Mn⁴⁺/Mn³⁺的比. 关键词： 价态 磁电阻 居里温度 金属—绝缘体转变     

The influence of Cr-content on curie temperature,crystallization temperature and room temperature electrical resistivity of Fe85−xCrxB15 metallic glasses

Amorphous ribbons of nominal compositions Fe_85-xCr_xB₁₅,_x =5, 10, 15 and 20 at%, were produced by a continuous liquid quenching technique. The Curie temperatures were measured using several methods. A quite large decrease with increasing Cr-content is observed: 20 K/at% Cr around 300 K. The Curie temperatures are compared with those of similar metallic glass systems based on Fe and Cr reported in the literature. The crystallization temperatures determined from measurements of the electrical resistivity versus temperature at a heating rate of ≈10K/min are obtained as a function of Cr-content, showing an increase in stability between 10 and 15 at% Cr. Finally, the room temperature (≈295K) electrical resistivities of as quenched and crystallized samples are given. The resistivity of the as quenched ribbons in nearly independent of Cr-content (≈128 μΩ cm) while the resistivity of the crystallized ribbons show an increase of ≈2.7 μΩ cm/at% Cr.     

直接利用磁场和温度精确确定磁性材料La0.67Ca0.33MnO3和Pr0.7Sr0.3MnO3的电阻率

电阻率是研究钙钛矿结构锰氧化物磁性材料的重要参数之一,它与温度和外加磁场有密切关系.本文的工作之一是寻找合适的方法,确定在金属-绝缘体转换过程中,不同磁场情况下,材料La0.67Ca0.33MnO3和Pr0.7Sr0.3MnO3的电阻率随温度变化的数学解析关系.通过非线性数值拟合,找到了满足这一关系的函数为双曲正切修正的高斯函数.同时,获得金属-绝缘体转换时居里温度Tc满足的微分方程以及与该温度对应的最大电阻率ρmax.本文的另一个工作是寻求最大电阻率ρmax和磁场之间的函数关系,发现采用玻尔兹曼函数可以精确反映两者之间的数学联系.两项工作得到的数学拟合结果与实验数据之间的最小相关系数为0.998,最大平均相对误差4.35％,说明数据拟合的结果与实验结果十分符合.     

Deposition of thin rhodium films by plasma-enhanced chemical vapor deposition

Thin films of rhodium have been prepared starting from dicarbonyl-2.4-pentadionato-rhodium(I), Rh(CO)₂C₅H₇O₂, by plasma enhanced CVD. The dependence of the deposition rate and film properties on substrate temperature, partial pressure of the organometallic and on hydrogen has been studied. Metal contents of 100% and thin-film resistivities as low as 5 times the bulk resistivity of rhodium have been achieved.     

Syntheses and characterization of polymer/TaS2 layered nanocomposites

Polymer/TaS₂ layered nanocomposites have been synthesized using the exfoliation–adsorption technique, using 1T-TaS₂, 2H-TaS₂, and 4Hb-TaS₂ single crystals hosts and poly(ethylene oxide) (PEO) and poly(ethylenimine) (PEI) as guest intercalates. Optimum conditions to synthesize nanocomposites were obtained for each set of TaS₂ polytypes and polymers using powder X-ray diffraction (XRD). XRD patterns showed that all nanocomposite materials contain polymer between all individual TaS₂ sheets. Although 1T-, 2H-, and 4Hb-TaS₂ polytypes are well known to show quite different temperature dependences of resistivity, the resistivities of all nanocomposites show similar temperature dependences.     

Electrical and thermal conductivity of soft solder at low temperatures

The electrical resistivity of soft solder (Pb_0.28Sn_0.72) has been measured in the temperature range 4.2 K to 300 K. The ‘alloy’ becomes electrically superconducting at a temperature of 6.9 K. Above this, in the entire temperature range, the resistivity could be described, apart from the residual resistivity, by the weighted average of the resistivities of the individual constituents which are derived from the Bloch-Grüneisen relation. The results are in accordance with the phase diagram, which shows a co-existence of two phases in almost the entire range of concentration of the Pb-Sn binary system. It has been shown that the thermal conductivity data on soft solder as well as on Pb_0.7Sn_0.3, both taken from literature, could be interpreted on the same basis, below and above the ‘superconducting transition temperature’. Recent results on other Pb-Sn systems are discussed in the light of this interpretation.     

Heat capacity and electrical resistivity of some lanthanide-nickel (LnNi5) compounds between 5 and 300°K

Results of heat capacity measurements for LnNi₅ compounds with Ln  La, Ce, Nd and Gd are presented for the temperature range 5–300°K. Electrical resistivities are given for the Ce, Nd and Gd compounds over the same temperature range. The heat capacities are consistent with the previously observed magnetic behavior of LaNi₅, CeNi₅ and NdNi₅. The La compound is a Pauli paramagnet and its heat capacity behavior is that of a solid exhibiting only vibrational and electronic excitation. CeNi₅ remains paramagnetic to 4°K and its C_p behavior closely resembles that of LaNi₅. NdNi₅ exhibits a A-type thermal anomaly peaking at 6·4°K, which is ascribed to the break-up of ferromagnetism. It also shows excess heat capacity at higher temperatures resulting from excitation in the crystal field spectrum. Results for GdNi₅, are unusual. Magnetic entropy is introduced over an anomalously wide range of temperature. The process culminates in two λ-type thermal anomalies peaking at 29·8 and 30·6°K, suggesting that the development of the cooperative phase occurs in two stages. The magnetic transformations are also evident in the resistivity-temperature behavior of NdNi₅ and GdNi₅, the loss of the spin-disorder resistivity being readily apparent in the former material. The usual thermodynamic properties are computed from the heat capacity data. Magnetic entropies of NdNi₅ and GdNi₅ at 300°K are observed to be 95 and 86 per cent, respectively, of R In(2J + 1).