Search results for "resistivity"

Novel phase transitions in B-site doped manganites

2005

We have examined the infrared reflectivity and the electrical resistivity of La 1-x [Sr(Ba)] x Mn 1-z [Cu(Zn)] z O 3 samples in ferromagnetic metallic and insulator regime. Several phase transitions are observed, the most obvious being the transition from a ferromagnetic metallic to a ferromagnetic insulator phase that is related to the formation of short-range orbitally ordered domains. The temperature T 1 of the phase transition is dependent on doping concentration and for optimally doped samples (∼32% of Mn 4+ ions) we have found T 1 0.93 T C .

Radiation effects in transparent ferroelectric ceramics

1997

Radiation of different types ((gamma) -rays, electrons, neutrons) and fluence has been used to study the defect processes as well as the change of physical parameters in PLZT X/65/35 (X equals 4.5 - 11 at.%) and PbSc 0.5 Nb 0.5 O 3 (PSN) ceramics and to evaluate critical irradiation conditions. Effects on optical (extinction) spectra and dielectric characteristics (polarization, thermal and frequency dependences of dielectric permittivity (epsilon) and losses), dependent on composition and state of phase and polarization have been analyzed by means of annealing in isochronic and prolonged time regimes. A gradual shift of extinction edge to longer wavelengths, reduction of polarization and (…

Crystallographic, electronic structure and magnetic properties of the GdTAl; T=Co, Ni and Cu ternary compounds

2000

Abstract Single phase GdCoAl, GdCuAl and single crystal GdNiAl samples of good quality were synthesized. The electrical resistivity, magnetization and AC susceptibility as a function of temperature revealed in all these compounds a ferromagnetic ordering at 100, 83 and 60 K, respectively. A magnetic transition, probably to a non-colinear structure was observed in GdNiAl at 31 K as well as the presence of the third magnetic transition at 14 K, while in the GdCuAl compound an evidence of similar transition was found at 23 K. In GdNiAl a transition between two different crystallographic phases of ZrNiAl-type was observed at 220 K. The transition was accompanied by rapid jumps of crystal lattic…

Magnetotransport Properties of Thin Films of Magnetic Perovskites

2007

In this article we show magnetotransport of two prototypical (nearly) half metallic perowskites La2/3Ca1/3MnO3 and Sr2FeMoO6. In a half metal the spin polarisation at the Fermi energy is complete and tunneling magnetoresistive devices of high sensitivity can be realized with small external magnetic fields. In the vicinity of the metal-insulator phase transition (MIT) temperature of the manganite an external magnetic field can induce ’colossal’ magnetoresistive effects. In the simple perovskites La1-x Ca x MnO3 the charge transport above the MIT is of polaronic nature. Hall-effect measurements on the compound La0.67Ca0.33MnO3 below the MIT show a compensated Fermi-surface consisting of elect…

Unprecedented pressure-driven metallization and topological charge transport in an anion radical salt

2021

Abstract The hybrid inorganic/organic closed π -stacking and soft lattice of a copper anion radial (Copper-7,7,8,8-tetracyanoquinodimethane) renders its electrical conductivity and structural modifications, which are susceptible to temperature and pressure. The geometry of its metal-ligand construction contemplates the concept of topology with a charge-transfer instability. A pressure-induced ionic-neutral phase transition occurs and accompanies an anomalously large electrical conductivity, carries topological charges, and possesses a low energy gap smaller than the Coulomb gap. X-ray absorption spectroscopy of the metal establishes the high electrical conduction by the topological charges.…

Pressure-induced structural and semiconductor-semiconductor transitions in Co0.5Mg0.5Cr2O4

2018

The effect of pressure on the structural, vibrational, and electronic properties of Mg-doped Cr bearing spinel $\mathrm{C}{\mathrm{o}}_{0.5}\mathrm{M}{\mathrm{g}}_{0.5}\mathrm{C}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$ was studied up to 55 GPa at room-temperature using x-ray diffraction, Raman spectroscopy, electrical transport measurements, and ab initio calculations. We found that the ambient-pressure phase is cubic (spinel-type, $Fd\overline{3}m$) and underwent a pressure-induced structural transition to a tetragonal phase (space group $I\overline{4}m2$) above 28 GPa. The ab initio calculation confirmed this first-order phase transition. The resistivity of the sample decreased at low pressures …

High Pressure Raman, Optical Absorption, and Resistivity Study of SrCrO4

2018

We studied the electronic and vibrational properties of monazite-type SrCrO4 under compression. The study extended the pressure range of previous studies from 26 to 58 GPa. The existence of two previously reported phase transitions was confirmed at 9 and 14 GPa, and two new phase transitions were found at 35 and 48 GPa. These transitions involve several changes in the vibrational and transport properties with the new high-pressure phases having a conductivity lower than that of the previously known phases. No evidence of chemical decomposition or metallization of SrCrO4 was detected. A tentative explanation for the reported observations is discussed.

2020

Abstract The structural stability and physical properties of CrVO4 under compression were studied by x-ray diffraction, Raman spectroscopy, optical absorption, resistivity measurements, and ab initio calculations up to 10 GPa. High-pressure x-ray diffraction and Raman measurements show that CrVO4 undergoes a phase transition from the ambient pressure orthorhombic CrVO4-type structure (Cmcm space group, phase III) to the high-pressure monoclinic CrVO4-V phase, which is proposed to be isomorphic to the wolframite structure. Such a phase transition (CrVO4-type → wolframite), driven by pressure, also was previously observed in indium vanadate. The crystal structure of both phases and the pressu…

Transport measurements under pressure in III–IV layered semiconductors

2007

PACS 61.50.Ks, 62.50.+p, 72.15.Jf, 72.80.Jc This paper reports on Hall effect, resistivity and thermopower effect measurements under high pressure up to 12 GPa in p-type γ-indium selenide (InSe) and e-gallium selenide (GaSe). The paper focuses on two applications of transport measurements under pressure: electronic structure and phase transition studies. As concerns the electronic structure, we investigate the origin of the striking differences between the pressure behaviour of transport parameters in both layered compounds. While the hole concentration and mobility increase moderately and monotonously in e-GaSe up to 10 GPa, a large increase of the hole concentration at near 0.8 GPa and a …

Effects of Oxygen Plasma on the Chemical, Light-Emitting, and Electrical-Transport Properties of Inorganic and Hybrid Lead Bromide Perovskite Nanocry…

2018

We show that oxygen plasma affects in different ways the structural, chemical, optical, and electrical properties of methylammonium and cesium lead bromide nanocrystals. Hybrid organic–inorganic nanocrystals were severely and quickly degraded by oxygen plasma at 50 W. Their photoluminescence was quenched with almost 100% loss of the initial quantum yield, which is linked to decomposition of the nanocrystals. Inorganic nanocrystals were more resistant to oxygen plasma in the same conditions. Despite a moderate loss of photoluminescence and electrical conductivity, oxygen plasma had a positive impact, removing unbound ligands and resulting in more ohmic behavior of the film. This paves the wa…