Pulse measurement of the I–V characteristics in Bi-2212 intrinsic junctions

Current-voltage (I–V) characteristics are studied in the intrinsic Josephson junctions of Bi₂Sr₂CaCu₂O_y single crystals. In order to examine the influence of self-heating, a current pulse (∼0.2 μsec) is applied to the mesas of 40 μmϕx0.15 μm patterned on the crystal. As a consequence, in contrast to small characteristic voltageV _c in the continuous-current measurement, theV _c data is found comparable to the BCS value. Moreover, theI–V curve is nearly ohmic forl>l _c , implying that the nonlinearity under the continuous current is due to heating. The quasiparticle resistance forT<T _c is also presented by an estimate from the characteristic voltage.     

Effect of high electric field on the dc conduction of TeO2-V2O5-MoO3 amorphous bulk material

Effect of high electric field on the dc conductivity of TeO₂-V₂O₅-MoO₃ amorphous bulk samples with different molar ratio of each component was investigated with gap-type electrode arrangement. At low electric fields, the current-voltage (I–V) characteristics has a linear shape, while at high electric fields (>10³ V/cm), bulk samples show nonlinear behavior (nonohmic conduction) and current-voltage characteristics shows increasing deviation from Ohm’s law with increasing current density. High-field effect of Pool-Frenkel type was observed at electrical fields about 10³−10⁴ V/cm. In addition, positive deviation from Pool-Frenkel effect was observed when a field higher than about 10⁴ V/cm was applied.     

Effect of pressure on turnover behaviour inI–V characteristic curves in GeTeSe chalcogenide glass

Summary Thick layers of GeTeSe chalcogenide glass have been prepared and subjected to conduction measurements under the effect of both temperature and pressure. The results of theI–V characteristics exhibit transition from high-resistance state to differential negative resistance state through a turnover point. The application of uniaxial pressure shows the similar effect of temperature on that behaviour. Both current and voltage at the turnover point depend on pressure and ambient temperature. The rise of temperature in the conduction path due to joule heating and application of uniaxial pressure as well as the reduction in the energy gap width (β=2.87·10⁻¹²eV/N m⁻²) are estimated and discussed at the turnover point. This behaviour is explained according to the orientation of dipoles randomly dispersed in viscous amorphous matrix.     

Effect of the “negative chemical” pressure on the temperatures of phase transitions in the TlInS<Subscript>2</Subscript> layered crystal

The temperature dependences of the permittivity of TlInS_{2(1 −x)}Se_2x solid solutions have been experimentally investigated in the temperature range including the points of structural phase transitions in the solid solutions. It has been established that the isovalent substitution of selenium for sulfur in the anion sublattice of the TlInS_{2(1 − x)}Se_2x solid solutions shifts the phase transition temperatures T _i and T _c toward the low-temperature range with a simultaneous decrease in the temperature interval of the existence of the incommensurate phase. The T-x phase diagram is constructed for the solid solutions under study and the coordinates are determined for a critical point (of the Lifshitz type) at which the lines T _i (x) and T _c (x) converge in the phase diagram. The pattern of the T-x phase diagram for the TlInS_{2(1 − x)}Se_2x solid solutions has been analyzed within the phenomenological model of a virtual crystal.     

Thermal conductivity of solid cyclohexane in orientationally ordered and disordered phases

Thermal conductivity Λ _P of solid cyclohexane is measured at a pressure P = 0.1 MPa in the temperature range from 80 K to the melting point, which covers the ranges of low-temperature orientationally ordered phase II and high-temperature orientationally disordered phase I. Thermal conductivity Λ _V is measured at a constant volume in orientationally disordered phase I. The thermal conductivity measured at atmospheric pressure decreases with increasing temperature as Λ _P ∝ T ^−1.15 in phase II, whereas Λ _P ∝ T ^−0.3 in phase I. As temperature increases, isochoric thermal conductivity Λ _V in phase I increases gradually. The experimental data are described in terms of a modified Debye model of thermal conductivity with allowance for heat transfer by both phonons and “diffuse” modes.     

Structural phase transitions in Pd0.8 Si0.2 and Pd0.75 Si0.20 Ag0.05 alloys observed by pac

The phase transition in the alloys Pd_0.8 Si_0.2 and Pd_0.75 Si_0.20 Ag_0.05 have been investigated through the quadrupole interaction of¹¹¹Cd impurities. The quadrupole interactions were measured by means of the TDPAC technique from room temperature up to about 870 K. The variation of the quadrupole interaction with temperature in the alloy PdSiAg shows aT ^3/2 dependence below and above 629 K, with coefficientsB=5.43(25)·10⁻⁵ K^−3/2 andB=3.70(15)·10⁻⁵ K^−3/2, respectively. This demonstrates that the alloy undergoes a phase transition around 629 K. The existence of two electric field gradients observed in the alloy PdSi,V _zz (1)=3.47(54)·10¹⁷ V/cm² andV _zz (2)=2.29(36)·10¹⁷ V/cm², indicates that there are two different¹¹¹Cd sites. The corresponding fractionsf ₁ andf ₂ strongly depend on temperature. Below 520 K, most¹¹¹Cd nuclei are subject to the higher EFGV _zz (1) (f ₁≈70%), whereas above 520 Kf ₁ falls rapidly to zero andV _zz (2) becomes dominant. The temperature dependences of thef ₁ andf ₂ reveal a picture of the phase transition between the two crystal structures.     

Effect of the ferroelastic order parameter on the formation of lead titanate-zirconate phases

A phase diagram identical to the x-T diagram for lead zirconate-titanate (PZT) solid solutions (PbZr_{1 − x} Ti _x O₃) was obtained on the basis of a statistical 12-minima model in the vicinity of the cubic phase boundary. The applicability of this model to the phase transitions in PZT is discussed.     

The superconductivity and metallurgy of C15 materials: Hf-V and Zr-V

Variation of theT _c as a function of composition for the C15 materials of the systems Hf−V and Zr−V was investigated. Samples in the as cast and annealed conditions were examined by x-ray and optical metallography. None of the samples was found to be of single phase. For the Hf−V system,T _c increases to a constant value of about 9 K for the compositions between 36 and 60 at. %V. A slight increase ofT _c between 60 and 70 at. %V and a degradation inT _c above 80 at. %V were observed. As cast materials show the maximumT _c value of 9.4 K. Deviations from stoichiometry and heat treatments produce considerable changes in the microstructures but have little effect onT _c . A slight enhancement ofT _c for the alloy containing 80 at. %V is explained by the pressure on V₂Hf due to V phase by the differential thermal contraction. For the Zr−V system, maximumT _c value of 8–6 K was observed for alloys having 20–66 at. %V in as cast condition. Heat treatments cause the lowering ofT _c . Results indicate that the preparation of ZrV₂ superconducting material will need more careful control than would be necessary for HfV₂.     

The effect of bias field on the value and temperature dependence of the piezoelectric coefficient d 31 in (1 ? x )Pb(Mg1/3Nb2/3)O3? x PbTiO3 ( x = 0.06, 0.13) single crystals

It is established that, as a result of application of even a small (∼0.5 kV cm⁻¹) bias field E, the maximum of the piezoelectric coefficient d ₃₁ in (1 − x)Pb(Mg_1/3Nb_2/3)O₃ − xPbTiO₃(x = 0.06, 0.13) crystals shifts from the Vogel-Fulcher temperature to the critical point in the E-T phase diagram of a given composition. The field dependence of the d ₃₁(T) peak magnitude has a maximum near the E values corresponding to the critical point. Original Russian Text ? A.S. Emelyanov, S.I. Raevskaya, F.I. Savenko, I.P. Raevski, M.A. Malitskaya, E.I. Sitalo, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 132–133.     

Intrinsic Josephson effects in 60-K phase YBCO thin film mesas

We fabricatedc-axis oriented meas on YBa₂Cu₃O_7−δ thin films. Columnar structures with an area of 20×20 μm² and a depth of 0.1 μm were formed on oxygen deficient films with a critical temperature (T _c ) of 64 K or less. The devices showed hysteretic I–V curves without any branches. The dependence of the critical current density on the temperature nearT _c is explained by the Ambegaokar-Baratoff relation.     

Capacitance spectroscopic study of the Si/HF-electrolyte interface

Thep-Si/HF-electrolyte interface was characterized by capacitance–voltage (C–V) and current–voltage (I–V) studies. At low frequency, the measured capacitance exhibits two maxima: one in the weak accumulation regime (around 0.8 V [SCE]) and the other in the strong accumulation regime (around 2.6 V [SCE]), both of which disappear at high frequency. The disappearance of the two capacitance maxima is attributed to the slow response of interface traps to high frequencies. The flat-band potential, V_FB, is found to be frequency dependent. The surface state densities corresponding to the two capacitance maxima are estimated to be 3.2×10¹¹ cm^-2 and 2.4×10¹¹ cm^-2, respectively. The in situ I–V characteristics distinguish pore formation, transition and electropolishing regions. Porous Si synthesized at 50 mA cm^-2 gives a broad photoluminescence peak around 2.04 eV at 300 K. Received: 4 September 2000 / Accepted: 9 February 2001 / Published online: 26 April 2001     

Operation of the EGA electron gun at high gas pressures

Summary This paper presents experimental results on the effects of increasing gas pressure on electron gun operations. The electron gun used is the gun EGA which has been developed for the TSS-1 mission. Various gases have been used with pressures in the range from 10⁻⁶ to a few times 10⁻³ mbar. The measurements, taken in a vacuum chamber, show a steady increase in the slope of theI–V characteristics of the gun when the pressure is increased, as a consequence of ionization phenomena induced by the electron beam. Further measurements have been taken of the overall current on a target at some distance from the gun itself. An attempt is also made at a theoretical calculation of the effects observed, based on simplified models.     

Effect of mixed glass formers on the crystallization kinetics in AgI–Ag<Subscript>2</Subscript>O–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–MoO<Subscript>3</Subscript> glassy superionic system

The crystallization and glass transition kinetics using differential scanning calorimetry (DSC) in 50AgI–33.33Ag₂O–16.67[(V₂O₅)_1−x –(MoO₃) _x ] superionic glassy system is discussed. Thermal stability of glass, studied using various criteria, does not vary significantly with glass former variation. However, the activation energies for structural relaxation (E _s) at glass transition temperature and crystallization (E _c) obtained using Moynihan and Kissinger, Matusita-Sakka formulations found to exhibit interesting trends with MoO₃ substitution in the glass matrix. It is noticed that the electrical conductivity (σ)–temperature (T) cycles obtained at a typical heating rate of 1 °C/min do exhibit significant thermal events. The conductivity after first heating cycle at room temperature is found to be increasing with MoO₃ content and maximum for x = 0.3 (~10⁻³ Ω⁻¹ cm⁻¹ at 30 °C) which is comparable to that of the host 50AgI–33.33Ag₂O–16.67V₂O₅ glassy system. The parameters obtained from σ–T plots and DSC scans do complement each other in a particular range of composition.     

Magnetic and structural transitions in La1−x Sr x MnO3: T-x phase diagram

The electrical conductivity, magnetic susceptibility, magnetization, and submillimeter (v=5∓20 cm⁻¹) permittivity and dynamic conductivity of La_1−x Sr _x MnO₃ (0≤x≤ 0.45) single crystals are investigated. The anomalies in the temperature dependences of these quantities are identified with diverse magnetic and structural phase transformations, including antiferromagnetic and ferromagnetic ordering, structural transitions between strongly distorted (Jahn-Teller) and weakly distorted (pseudocubic) orthorhombic phases, structural transitions to a rhombohedral phase and unusual transitions to a polaron-ordering state. As a result, the complete T-x phase diagram of the system La_1−2x Sr _x MnO₃ is constructed in a wide interval of temperatures T=4.2∓1050 K and concentrations x=0−0.45. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 331–336 (25 August 1998)     

Dependences of the dielectric and pyroelectric properties of (1 ? x)PbFe1/2Nb1/2O3?xPbTiO3 ferroelectric ceramics solid solutions on the PbTiO3 content in a compositional range of 0 ≤ x ≤ 0.08

(1 − x)PbFe_1/2Nb_1/2O_3−x PbTiO₃ (PFN-xPT) ferroelectric ceramics with low dielectric loss and pronounced anomalies of dielectric and pyroelectric properties near the ferroelectric-ferroelectric phase transition was obtained by doping with lithium. The temperature dependence of the position of the morphotropic boundary between the rhombohedral (monoclinic) and tetragonal phases in the x-T phase diagram of the PFN-xPT system was determined for the first time.     

Paramagnetic relaxation of Er in an Er single crystal

The paramagnetic relaxation of Er in an Er single crystal was measured atT≫T _N and compared to the relaxation of Er ions in a polycrystalline Pb host. The results indicate an enhancement of at most 50% of the f-conduction electron exchange interaction in Er, as expected for highly ionic f-orbitals. The ratio of the quadrupole moments of the¹⁵⁴ Er(I ^π=11⁻) and the¹⁵⁵ Er(I ^π=13/2⁺) isomers was measured to be 1.18(3) indicating onset of nuclear deformation at N=87. Deceased May, 1986     

EPR studies of Cu2+ and V4+ ions in phosphate glasses

Two lead-phosphate glass systems doped with both copper and vanadium ions in different ratios were studied by EPR (electron paramagnetic resonance) method. EPR spectra and parameters (g_‖ = 2.44, g_⊥ = 2.08 andA _‖ = 117.6 · 10⁻⁴ cm⁻¹) obtained for x(CuO · V₂O₅)(l−x)[2P₂O₅ · PbO] glasses withx ≤ 10 mol% suggest a tetrahedral (Td) coordination of Cu²⁺ ions and not a tetragonally elongated octahedron as has been assumed in previous works. The ground state of the paramagnetic electron is thed _xy copper orbital with a 4p_z contribution of 6%. For 20 ≤x ≤ 40 mol% a broad line (ΔB = 307 G) characteristic for clustered ions appears atg = 2.18. The V⁴⁺ ions are evidenced only in the spectra of x(CuO · 2V₂O₅)(1 −x)[2P₂O₅ · PbO] glasses and the resonance parameters suggest a pentacoordinated C_4v local symmetry for these ions. The hyperfine structures characteristic for Cu²⁺ and V⁴⁺ ions disappear for 10 ≤x ≤ 40 mol% due to the mixed exchange Cu²⁺−V⁴⁺ pair formation in these glasses.     

Spin-orbit coupling,spin-lattice relaxation,and spin-memory studies ofF-center-molecular-ion pairs in alkali halides

Summary The spin-orbit parameter Δ, spin-lattice relaxation timeT ₁, and spin-mixing parameter ɛ ofF _H(OH⁻) andF _H(CN⁻) centers in several alkali halides have been studied with magnetic circular dichroism at ∼2 K. A close comparison of the experimental results before and after optically induced association of theF center with the molecular ion has been made. In crystals of NaCl structure the negative spin-orbit parameter Δ changes little betweenF andF _H centers in the same host. For CsCl and CsBr two values of Δ have been derived forF _H(CN⁻) centers with axis parallel or perpendicular to the magnetic field. In all studied systems, the spin-lattice relaxation timeT ₁ is already shorter before aggregation compared toF formation. The spin-mixing parameter ɛ decreases slightly forF _H(OH⁻) compared toF centers, while it increases drastically forF _H(CN⁻) defects and reaches its maximum possible value ɛ=0.5 in cesium halides. First attempts to interpret these magneto-optical results will be presented. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

NMR study of the magnetic properties and electronic structure of amorphous Ni−B−P alloys

The¹¹B and³¹P NMR Knight shift (K) and Korringa spin-lattice relaxation rate (1/T ₁ T) have been measured for amorphous Ni_81.5B_18.5−x P _x alloys with 0≤x≤18.5. In accordance with previous bulk measurements, the³¹P NMR parameters vary markedly with composition whereas the¹¹B NMR parameters remain almost constant except for small P-contents. It is suggested that the d-band contribution toK(³¹P) is positive and that toK(¹¹B) is negative. The data further support our previous conclusion that amorphous Ni_81.5B_18.5 is a Pauli paramagnet rather than a weak itinerant ferromagnet.     

Measurement of atomic parameters for the3 D 1 state of I–II

The decay rates of the³ D ₁ level of I–II and the 3s ₂ level of neon have been measured by the magnetic-field power dip method. The decay rate at the zero-pressure limit is found to be 7.1 MHz/2π for the³ D ₁ level. The collision cross-section for excited I ions with helium atoms equals 0.19×10⁻¹⁵ cm². This work was supported by project MR-1.5-1.05.