Temperature Dependence Of In-plane Research Articles

Single Crystal Growth of the Fe-based Superconductor and Related Materials Using the High Pressure Synthesis

In the first half of this article, the new material search for FeX4 (X=pnictogen, chalcogen) based superconductors is introduced and the new method to grow single crystals for Fe-based superconductors and related materials are also described. Using a high-pressure apparatus, we report the single crystal growth of Fe-based superconductors and related materials (BaFe2As2, SrFe2As2, (Ba, Na)Fe2As2 and α-PbO type FeSe0.9 superconductor, BaNi2P2). Especially, we have grown single crystals of BaNi2P2 superconductors from stoichiometric composition solutions for the first time. The temperature dependence of in-plane (r//) and out-of-plane (r⊥) resistivity for BaNi2P2 crystals were measured, the anisotropy ratio r⊥/r// is ~6.3 at 300 K, and sharp superconducting transition was observed at ~2.5 K.

Anisotropic electrical transport studies of Ca 3Co 4O 9 single crystals grown by the flux method

Single crystals of cobaltite Ca 3Co 4O 9 having sizes up to 10×6×0.2 mm 3 were grown by the flux method. The morphology, structure and composition of the crystals were analyzed by scanning electron and atomic force microscopy, X-ray diffraction and energy-dispersive X-ray analysis, respectively. The results revealed that stoichiometric single crystals of Ca 3Co 4O 9 grow via a two-dimensional layer-by-layer mechanism. The temperature dependences of in-plane ( ρ ab ) and out-of-plane ( ρ c ) electrical resistivities were measured in the temperature range 30–300 K. ρ ab ( T ) exhibited a metal-to-semiconductor transition at around 80 K. Analysis of the semiconducting region revealed the opening of an energy gap of ∼10 meV. On the other hand, ρ c ( T ) showed semiconducting behavior over the whole temperature range with a crossover from 3D to 1D variable range hopping conduction at ∼120 K. The temperature dependence of magnetization revealed two transitions at 30 and 19 K.

Anisotropy in thermo-optic coefficients of polyimide films formed on Si substrates

The temperature dependence of in-plane and out-of-plane refractive indices (i.e., thermo-optic coefficients dn/dT) was measured for seven kinds of aromatic polyimide (PI) films formed on silicon substrates. The absolute values of dnTE/dT (polarization parallel to the film plane) are significantly larger than dnTM/dT (perpendicular to the film plane). The dn/dT for average refractive indices (nav) are −94 to −58 ppm/K, independent of film thickness. The anisotropies (dnTE/dT−dnTM/dT) are −9 to −39 ppm/K. Although the values of nav are independent of film thickness, the anisotropies slightly increase as the film thickness decreases for flexible PI films. As expected from the temperature derivative of the Lorentz–Lorenz (LL) equation, the amorphous PI films exhibiting high nav show large dnav/dT, however, significant anisotropies are observed even for the PI films exhibiting very small birefringence.

Temperature dependence of midinfrared peaks in high-Tc perovskites.

The temperature dependence of midinfrared spectra \ensuremath{\sigma}(\ensuremath{\omega},T), the Hall coefficient ${\mathit{R}}_{\mathit{H}}$(T), and thermoelectric power S(T) have been calculated on the basis of a two-fluid model consisting of localized polarons and delocalized carriers. It is shown that in the case of intermediate polarons, the in-plane temperature dependence of \ensuremath{\sigma}(\ensuremath{\omega}) is determined by the thermal activation energy and can both increase and decrease with temperature in agreement with the observed results. The same charge carriers were used to calculate ${\mathit{R}}_{\mathit{H}}$(T) and S(T). The temperature dependence of the Hall coefficient and thermoelectric power is determined by the same thermal activation energy and the agreement with experiments is good.

Electron Transport Properties of UAsSe

There is a great interest in some group of uranium and cerium compounds consisting of increasing number of members subsequently termed as anomalous, intermediate valence, Kondo's lattice, and heavy fermions systems. This group has been extended to systems whose well-known members are CeNiSn and Ce3Bi4 Pt3 compounds. They are termed as hybridization gap — or semiconducting mixed valence — compounds [1, 2]. We will show that some features of electron transport behaviour of UAsSe correspond to the systems mentioned above. The UAsSe crystallizes in tetragonal (P4/nmm) structure. It becomes uniaxial and highly anisotropic ferromagnet below 113 K with spontaneous magnetic moment along c-axis [3]. Its temperature dependence of in-plane (1 c) resistivity (p(300) = 280 μS2 cm) and magnetoresistivity are already known [4, 5]. We will present the temperature variation of resistivity anisotropy, in-plane thermoelectric power and the Ball coefficient. Plate-like single crystals of UAsSe, of thickness up to 0.5 mm and other dimensions up to 10 mm, were grown by chemical vapor transport method. The Hall coefficient as well as the thermoelectric power were measured by conventional dc methods on samples whose length exceeds the width more than three times. The resistivity anisotropy was measured by Montgomery's modification of the van der Pauw method on rectangular sample with dimensions of 0.83 x 0.25 x 0.29 mm 3 along a-, band c-axes, respectively. Four silver wires were soldered with indium to the sample corners in the ac plane to determine the resistivity tensors along sand c-axis. Temperature dependence of the resistivity tensors is shown in Fig. 1. The Curie temperature, Tc, is equal to 102 ± 0.5 K for this crystal. It was determined by the maximum of dp a /dT. It can be compared with Tc = 109 K determined

Preparation and characterization of a new composite-layered sulfide, (PbS) 1.12VS 2, “PbVS 3”

(PbS) 1.12VS 2, “PbVS 3”, a new composite-layered sulfide, has been prepared and characterized using X-ray powder diffraction, electron diffraction, preliminary single crystal structure determination, and resistivity measurement. The structure is composed of two kinds of mutually stacked layers: pseudo-tetragonal two-atom-thick PbS layers with distorted NaCl type and pseudohexagonal three-atom-thick octahedrally-coordinated 1T-VS 2 sandwiches. Both the lattices of PbS and VS 2 have monoclinic subsystem whose periodicities match along the a and c axes but not along the b axis. The composition of “PbVS 3” has been determined to be (PbS) 1.12VS 2 on the basis of preliminary single crystal structure determination. The temperature dependence of inplane(ab-plane) resistivity of “PbVS 3” shows a semiconducting behavior.