B. T. Melekh

Structure, phase transitions and optical properties of pure and rare earth doped BaCeO3, SrCeO3 prepared by inductive melting

Fused crystalline BaCe1−xLnxO3−δ (Ln=Y,Gd,Nd, 0<x<0.2), and SrCe1−xDyxO3−δ (x=0; 0.05) have been prepared by inductive melting. XRPD measurements have showed that annealed BaCeO3 was orthorhombic. DSC spectra of BaCeO3 have showed two peaks at 533 K and 630 K. Phase transitions in the range 270–900 K were not revealed in BaCe0.8Y0.2O3−δ, BaCe0.9Nd0.1O3−δ and SrCeO3. For comparison ceramic BaCeO3:Gd was considered. Raman spectra of BaCeO3 have confirmed the X-ray data on the orthorhombic symmetry for annealed samples. Eu-luminescence study of BaCeO3:(Y+Eu) has confirmed the octahedral oxygen enviroment of trivalent dopant ions.

CeAlO3 crystals: Preparation and study of their electrical and optical characteristics

Crystals of cerium aluminate with perovskite structure were obtained using the cold-crucible technique. The electrical and optical properties of cerium aluminate were studied in air in the range 300–1300 K. The main characteristics of CeAlO3 at T=300 K are a follows: electrical conductivity σ=10−7 S/cm, dielectric permittivity ɛ=3000–10000 (both measured at a frequency of 1000 Hz), thermal band-gap width ΔE=2.3±0.5 eV, and optical width δE=2.65±0.25 eV, which decreases at a rate of −0.62×10−3 eV/K with increasing temperature in the 300-to 1500-K interval.

Conductivity, magnetoresistance, and specific heat of oxygen-deficient La0.67Sr0.33MnO3−α (0≤α≤0.16)

Oxygen-deficient La0.67Sr0.33MnO3−α solid solutions have been studied. A comparison is made with the results obtained in an earlier study of a similar lanthanum-calcium manganite series. The physical characteristics of both series are accounted for as being due to a change in the Mn3+/Mn4+ ratio caused by oxygen removal. The differences between the strontium and calcium series originate from differences in both the bulk properties of the original oxygen-stoichiometric materials and their texture. In the strontium series, the texture manifests itself in intergrain magnetoresistance, which exceeds in magnitude the colossal magnetoresistance caused by bulk properties of the material. Study of the oxygen-deficient La0.67Sr0.33MnO3−α compound revealed specific features in the dependence of the electrophysical parameters on temperature and the Mn4+ fractional content that were not observed in the La0.67Ca0.33MnO3−α compound studied by us earlier and in La1−xSrxMnO3 samples described in the literature. The physics underlying these differences is discussed. A modified phase diagram relating the phase transition temperature to the Mn4+ fraction is proposed.

Spectroscopic evidence of a mixed valence charge compensation in the process of proton intercalation into BaCeO3

Abstract Barium cerate (BaCeO 3 ) is a parent material for the family of high-temperature protonic conductors. Nowadays, BaCeO 3 -based materials were accessible in ceramic form. Recently, pure and doped BaCeO 3 were obtained in crystal form, and this gives an ability for more reliable study of microscopic aspects of hydrogen intercalation. This paper is devoted to study the details of proton intercalation process by luminescent and IR absorption spectroscopy. In this study, it was shown for the first time that charge compensation in the process of proton incorporation in undoped barium cerate is provided by mixed valence state of cerium ions.

Calorimetric study of phase transitions in the perovskite BaCeO3

Differential scanning calorimetry was used to study phase transitions (PT) in the perovskite BaCeO3. It is shown that its phase state is determined by a second-order λ transition at Ttr=520–540 K and a first-order δ transition at Ttr=600–670 K. Differences in PT parameters between ceramic and fused BaCeO3 have been established.

Luminescence spectra of nominally pure BaCeO3 perovskite crystals

Luminescence spectra of barium cerate BaCeO3, a starting material in the family of mixed conductors with protonic and oxygen conduction, are studied for the first time. The photoluminescence of this material is shown to be due to transitions involving cerium ions. A model of the recombination process is proposed. The luminescence of samples subjected to various post-growth treatments is measured, and the connection between the type of the treatment and the specific changes in the luminescence spectra is interpreted.

X-ray emission studies of evolution of the electron and spin structures of Mn in mixed manganites Ln1 − xSrxMnO3 (Ln = La, Sm, and Ce)

The chemical shift

Nonmonotonic temperature dependence of critical current in superconducting Fe(Se0.3Te0.7)0.82 crystals

\Delta E_{K_{\beta 1} }