Temperature dependence of the electric field gradient in AgIn2 intermetallic compound

The temperature dependence of the electric field gradient in the AgIn₂ intermetallic compound was measured using the TDPAC technique. From 80 K up to 415 K a linear dependence was found. Below 80 K a change in this behaviour was observed. This and previous results are interpreted as related to optical-phonon modes in intermetallic compounds.     

Quadrupole interaction in In0.95 Ag0.045 Ga0.005 alloy

The temperature dependence of the quadrupole interaction of¹¹¹Cd in the In_0.95 Ag_0.045 Ga_0.005 alloy is determined by the time differential perturbed angular correlation method from 77 to 422 K. The electric field gradients produced by the lattice are derived. The temperature dependence of the electric field gradient is found to follow theT ^3/2 law observed in In between 77 K and room temperature and to deviate from it at higher temperatures. The widths of the electric field gradient distribution are 0.1147(259), 0.0924(340), 0.4954(601) and 1.344(175) at 77, 298, 373 and 422 K, respectively. This illustrates that the alloy is well ordered at 77 and 298 K and that it becomes less ordered at 373 and 422 K.     

Nuclear quadrupole interaction in the low dimensional hf-trichalcogenides

We report on Time Differential Perturbed Angular Correlation measurements of the nuclear quadrupole interaction of¹⁸¹Hf(β⁻)¹⁸¹ and its temperature dependence in the low dimensional Hf- trichalcogenides HfS₃, HfSe₃ and HfTe₃. In HfS₃ the temperature dependence of the precession frequency is a slowly decreasing function with a negative curvature, the deviation from axial symmetry of the electric field gradient is practically temperature independent. In HfSe₃ the NQI shows a peculiar behaviour; between 10K and 300K the quadrupole frequency and the asymmetry parameter increase, between 300K and 400K the frequency decreases while the deviation from axial symmetry increases, indicating a structural phase transition near room temperature. In HfTe₃ the quadrupole frequency is practically temperature independent below 600K and increases linearely at higher temperatures, the asymmetry parameter increases steadily in the temperature range from 10K to 600K and then decreases. There is a strong correlation between the strength and the asymmetry of the electric field gradient so that the system depends on one control parameter only.     

Pressure dependence of the electric field gradient in the AgIn2 intermetallic compound

The pressure dependence of the electric field gradient (EFG) in the AgIn₂ intermetallic compound was measured from zero up to 35 kbar using the time differential perturbed angular correlation technique in¹¹¹Cd. The unit cell volume and thec/a ratio variations with pressure were measured up to 80 kbar. The temperature dependence of the cell parameters was also measured, in a range varying from 300 K up to 458 K. The relationship of these results showed that the contribution of the lattice thermal expansion to the EFG variations is about 1/3, a small but not negligible part. The estimated EFG volumetric dependence is at variance with the systematic results found in pure metals. Work supported in part by FINEP and CNPq (Brasil).     

Temperature dependence of the electric field gradient in CdSe and HfO2

The time differential perturbed angular correlation technique was applied to study the electric field gradient in the semiconductor CdSe and the insulator HfO₂ at different temperatures. Whereas the semiconductor CdSe shows an increasing quadrupole coupling constant with increasing temperature, the insulator HfO₂ exhibits no temperature dependence of the electric field gradient over the whole temperature range investigated.     

Electric field gradients at the 111In site in the ferroelectric and paraelectric phases of LiTaO3

The temperature dependence of the electric-field gradient of ¹¹¹Cd in single crystalline LiTaO₃ was studied from room temperature to 1040 K in the ferroelectric and paraelectric phases. The data taken at room temperature show unambiguously the presence of two quadrupole interaction frequencies, ν_Q1=230 MHz and ν_Q2=242 MHz, with nonzero asymmetry parameters, while above the Curie temperature (T_C=878 K) the data are well described by a unique frequency. The electric field gradient shows a usual temperature dependence, increasing aproximately in a linear fashion until T_C and then decreasing faster. The initial increase is explained mostly by the lattice expansion, while above T_C it is necessary to consider Li and O displacements. This revised version was published online in August 2006 with corrections to the Cover Date.     

Paramagnetic fluctuations in Yb3Ga5O12 investigated with 172Yb PAC probe

¹⁷²Yb PAC measurements were carried out on Yb₃Ga₅O₁₂ at temperatures ranging from 14 to 1100 K. The time dependent hyperfine interaction is clearly evident below room temperature. It is attributed to spin fluctuations of Yb ion in the ground state of the ²F_7/2 multiplet. Above 500 K, the temperature dependence of the electric field gradient is shown to result from a varying population of the crystal electric field levels. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature dependence of the electric quadrupole interaction at scandium impurities in zirconium and hafnium

The PAC probe⁴⁴Sc was employed to study the magnitude and temperature dependence of the electric quadrupole interaction at the site of the transition metal Sc in the hexagonal host lattices Zr and Hf. In Zr ∼ 100% of the probe atoms were situated on regular lattice sites and a quadrupole interaction frequency of υ_Q=7.8(1)MHz was measured at room temperature. For Hf the fraction of the probe atoms on regular lattice sites was smaller and a damping of the interaction pattern (υ_Q=9.3(5)MHz at 293 K) could not be excluded. The temperature dependence of the electric field gradient in both host lattices was found to be weak.     

Response of the capacitance and dielectric loss of the SrRuO<Subscript>3</Subscript>/SrTiO<Subscript>3</Subscript>/SrRuO<Subscript>3</Subscript> film heterostructures to variations in temperature and electric field

Three-layer epitaxial heterostructures with a 750-nm-thick intermediate strontium titanate layer between two strontium ruthenate conductive thin-film electrodes have been grown by laser deposition. Photolithography and ion etching have been used to form film parallel-plate capacitors based on the grown heterostructures. The capacitance (C) and dielectric loss tangent (tanδ) of the parallel-plate capacitors have been measured in the temperature range T = 4.2–300 K at an applied bias voltage of up to ±2.5 V and without it. At T > 100 K, the temperature dependence of the dielectric permittivity (ε) of the SrTiO₃ intermediate layer is well approximated by the Curie–Weiss law taking into account the capacitance induced by the penetration of an electric field into the oxide electrodes. At T ≈ 20 K, the dielectric permittivity ε of the SrTiO₃ intermediate layer decreases by approximately 20% in an electric field of 25 kV/cm. The dielectric loss tangent of the film capacitor heterostructures decreases monotonically with a decrease in the temperature in the range from 300 to 80 K and almost does not depend on the electric field strength. However, in the range from 80 to 4.2 K, the dielectric loss tangent increases nonmonotonically (abruptly) with a decrease in the temperature and decreases significantly in an applied electric field.     

Electrical properties of microcrystalline Sc3N@C80 fullerene

The electrical properties of microcrystalline Sc₃N@C₈₀ fullerene with fcc structure are studied by measuring both d.c. conductivity temperature dependence and a.c. impedance. Below 450 K the Sc₃N@C₈₀ sample has an energy band gap of 1.71 eV, which does not depend on the strength of the applied electric field. But when the temperature is above 450 K, a phase transition which results in a small band gap of 1.22 eV occurs under electric field strengths larger than 1 kV/cm. We also found from Cole–Cole plots of a.c. impedance that the contact resistance at the Au/Sc₃N@C₈₀ interface is less than that at the Au/C₆₀ interface.     

Cd-Impurities in the semiconductor in2Te5 studied by the PAC-method

The temperature dependence of the electric field gradient at a Cd acceptor atom in the semiconductor In₂Te₅ was measured with the PAC-method. The results are explained in a bond-switching model.     

75As N.Q.R. and 19F N.M.R. study of solid AsF3

The temperature dependence of the ⁷⁵As pure quadrupole resonance frequency in AsF₃ has been studied from 77 K to a temperature very close to the melting point. It is found that the effective electric field gradient at the As site does not shift much from the gas-phase value and that the temperature dependence of the ⁷⁵As N.Q.R. frequency seems to follow the Bayer-Kushida model. The occurrence of a line-width transition in the ¹⁹F N.M.R. spectrum between 200 and 150 K demonstrates the presence of low-frequency, large-amplitude molecular motions which are too slow to average out the ⁷⁵As quadrupole coupling.     

Temperature behavior of the order parameter in Pb5Ge3O11

The temperature dependence of the spontaneous polarization in the Pb₅Ge₃O₁₁ lead germanate (PGO) is experimentally investigated using optical, magnetic resonance, and conventional electrical measurements. The deviations from the temperature dependence typical of second-order phase transitions at temperatures below 420 K are explained in terms of incomplete polarization switching and polarization induced by a residual depolarization field. The low-temperature anomalies are interpreted without consideration of additional structural transformations. The internal bias field is determined from the experimental temperature dependence of the perfect polarization of PGO single crystals in an electric field.     

The temperature dependence of the nuclear quadrupole interaction of 44Ti(EC)44Sc in rutile

The temperature dependence of the Nuclear Quadrupole Interaction on ⁴⁴Sc in rutile was measured by Time Differential Perturbed Angular Correlation in the temperature range from 300 K to 945 K. Whereas $\upomega _{\rm Q} = \mathrm{eQV}_{\rm zz}/4\rm \hbar$ with V_zz denoting the largest component of the electric field gradient tensor in magnitude increases with increasing temperature, the asymmetry parameter η remains essentially constant. This observation fits into the systematic with other probes provided the sign of V_zz is negative.     

硫酸锂钾的室温相和低温相的锂离子位置

核磁共振实验表明,LiKSO₄在T_c=195K发生结构相变。本文报道了温度低于T_c时,Li位电场梯度张量的温度依赖关系。结合理想离子晶体模型,讨论了该晶体的结构,指出室温相Li的位置并不像Bradley所推测的,在(2/3,1/3,0.849)的位置,而应在(2/3,1/3,0.706)的位置;195K的相变是由于Li离子的位移造成;低温相的空间群可能为R3。 关键词：     

The temperature dependence of the magnetic hyperfine field of tantalum in dysprosium

The temperature dependence of the magnetic and electric hyperfine interactions at the site of ¹⁸¹Ta impurities in polycrystalline Dy has been measured between 4.2 and 178 K using the time differential perturbed angular correlation technique. The value of the magnetic hyperfine field at 4.2 K is: |H_hf(TaDy)| = 212(9) kG The temperature dependence of the magnetic hyperfine field follows closely the prediction of the molecular field model.     

Converse flexoelectric effect in the SrTiO3 single crystal

The converse flexoelectric effect in the SrTiO₃ single crystal as a response of inhomogeneous strain (bending strain) to an applied electric field has been studied. The temperature dependence of the effect in the temperature range of 77–450 K has been obtained.     

LiKSO4低温相变的核磁共振研究

研究了LiKSO₄中⁷Li的核磁共振谱与温度及晶体取向的关系。证实了在T_c=195K存在一个结构相变,并由实验数据推导出在这一温度以下,晶体的对称性低于P31c,每单胞至少含有六个分子式。没有证据说明有一个无公约相存在。测得181K的四极耦合常数为38.9kHz,不对称因子η=0.46,电场梯度主轴方向z与原c轴成11.6°角。 关键词：     

Pressure and temperature dependence of the electric field gradient (EFG) in CdS

Using the time differential perturbed angular correlation technique (TDPAC), the electric hyperfine interaction of¹¹¹Cd in the II-VI-semiconductor CdS was investigated. The results of the temperature and pressure dependence of the electric field gradient (EFG) are discussed. The binding energyE _b for¹¹¹In at a Cd lattice site and a Cd vacancy (¹¹¹In_Cd–V_Cd–pair) could be estimated to 340 meV±80 meV by means of an Arrhenius-Plot. The disappearance of the 79 MHz and 73 MHz frequencies under a pressure of about 30 kbar could be due to their vacancy character or to the beginning of the phase transition to rocksalt structure.     

Thermal evolution of the electric field gradient at 181 Ta in αHfNi

The perturbed angular correlation method has been employed to study the temperature dependence of the ¹⁸¹Ta hyperfine interaction parameters in the polycrystalline intermetallic compound αHfNi. At ambient temperature the frequency of the electric quadrupole interaction was ω _Q = 26.0(2) Mrad/s and the asymmetry parameter η = 0.22(1). The magnitude of the observed electric field gradient decreases with increasing temperature from 78 to 900 K. The calculations were done using the augmented plane wave plus local orbitals method as implemented in the WIEN2k code, using the generalized gradient approximation. In addition, a supercell calculation with Ta impurity located at the hafnium site was performed. The obtained result is in a good agreement with the experiment.