Search results for "Perovskite"

Local structure of A-atom in ABO3 perovskites studies by RMC-EXAFS

2020

The measurements of Sr K-edge XAFS were performed under the approval of Proposal No. 97G042 of Photon Factory (KEK) and partially supported by the Research Grants of Hirosaki University. This work was supported by Bruce Ravel providing data for BTO. Boby Joseph acknowledges IISc Bangalore and ICTP Trieste for financial support through the award of the IISc-ICTP fellowship.

<title>Large-scale first-principles calculations of Fe-doped SrTiO<formula><inf><roman>3</roman></inf></formul…

2003

The energy level positions in the optical gap and atomic geometry for the Fe4+ impurity substituting for a host Ti atom in SrTiO3 are calculated using the Unrestricted Hartree-Fock (UHF) method and supercells containing up to 320 atoms. In agreement with experiment, the high spin (S = 2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacements of six nearest O ions which is a combination of the Jahn-Teller and breathing modes. A considerable covalent bonding between the Fe ion and four nearest O ions takes place. We predict a strong dependence of optical absorption energies on the crystal compression or internal tensi…

<title>Photostimulated recombination processes in x-irradiated CsCdF<formula><inf><roman>3</roman></inf></form…

2005

Fluoride crystals with the perovskite structure doped with rare-earth ions and other activators are interesting materials for laser hosts, scintillators, and detectors of ionizing radiation. Therefore, an actual task is to clarify the structure of the radiation-induced defects and recombination processes in these crystals. Compared to other fluoroperovskites, considerably less information is available concerning to the radiation-induced processes in the CsCdF3 crystals. We present a study of photostimulated luminescence (PSL) in the previously x-irradiated CsCdF3 crystal doped with Mn (0.05%). After the x-irradiation of the crystal, optical stimulation at 320 nm leads to the appearance of 3…

Hybrid DFT calculations of theFcenters in cubic ABO3perovskites

2008

We employed the hybrid DFT-LCAO approach as implemented in the CRYSTAL code for 135 atom supercell calculations of O vacancies with trapped electrons (known as the F centers) in three cubic perovskite crystals: SrTiO3, PbTiO3 and PbZrO3. The local lattice relaxation, charge redistribution and defect energy levels in the optical gap are compared. We demonstrate how difference in a chemical composition of host materials leads to quite different defect properties.

Ab initio calculations of SrTiO3, BaTiO3, PbTiO3, CaTiO3, SrZrO3, PbZrO3 and BaZrO3 (001), (011) and (111) surfaces as well as F centers, polarons, K…

2014

In this paper, the review of recent results of calculations of surface relaxations, energetics, and bonding properties for ABO 3 perovskite (001), (011) and (111) surfaces using mostly a hybrid description of exchange and correlation is presented. Both AO and BO 2-terminations of the nonpolar (001) surface and A , BO , and O terminations of the polar (011) surface, as well as B and AO 3-terminations of the polar (111) surface were considered. On the AO -terminated (001) surface, all upper-layer A atoms relax inwards, while all second layer atoms relax outwards. For the BO 2-terminated (001) surface, in most cases, the largest relaxations are on the second-layer metal atoms. For almost all …

The Effect of Oxygen Vacancies on the Atomic and Electronic Structure of Cubic ABO3Perovskite Bulk and the (001) Surface:Abinitio Calculations

2009

We employed the hybrid DFT-LCAO and GGA-PW approaches as implemented in the CRYSTAL and VASP codes, respectively, for large supercell calculations of neutral O vacancies with trapped electrons (known as F centers) in the bulk and on the (001) surface of three cubic perovskite crystals (SrTiO 3 , PbTiO 3 , and PbZrO 3 ). The local lattice relaxation, charge redistribution, and positions of defect energy levels within the band gap are compared for three perovskites under study. We demonstrate how the difference in chemical composition of host materials leads to quite different defect properties.

Single-Exciton Amplified Spontaneous Emission in CsPbX3 (X = Br, I) Perovskite Nanocrystals

2019

Crystal chemistry and redox behaviour of antimony strontium calcium perovskites

2000

The compound Sr2Sb1.4Ca0.6O6 and their reduced forms Sr2Sb1.4Ca0.6O5.17 and Sr2Sb1.4Ca0.6O4.84 have been prepared and characterized by powder X-ray diffraction, electron diffraction, iodometric analyses and thermogravimetric analysis. The three phases with different oxygen stoichiometries are structurally related to the perovskite and show symmetry distortions from the ideal cubic structure (with cell parameter ap). The crystal structure of Sr2Sb1.4Ca0.6O6 may be refined by the Rietveld method from powder X-ray diffraction data using the space group P21/n, and the cell parameters a=5.776(2), b=5.7837(2), c=8.1718(3) A, β=90.039(3)° with the same structural model than for previously studied …

Structural effects of Co and Cr substitution in LaMnO3 + δ

2000

Series of perovskite oxides with the composition LaMn1 − xMxO3 + δ (M = Cr, Co; 0 ≤ x ≤ 1) have been synthesized by thermal treatment of precursors obtained by freeze-drying of acetic acid solutions. The oxides have been characterized by X-ray diffraction, and the Mn4+ content and, thus, the oxygen excess, δ, has been determined by redox back-titration. LaMnO3.14 and LaCrO3 phases have the rhombohedral-LaAlO3 and the orthorhombic-GdFeO3 structures, respectively. The LaMn1 − xCrxO3 + δ phases have the rhombohedral structure for x ≤ 0.3, and the orthorhombic structure for x ≥ 0.5. LaCoO3 has, as LaMnO3.14, the rhombohedral structure. However, the LaMn1 − xCoxO3 + δ phases have orthorhombic st…

Magnetic Transitions in the Double Perovskite Sr2FeRe1-xFexO6(0≤X≤0.5)

2008

AbstractThe synthesis, structure, and magnetic and transport properties of solid solutions Sr2FeRe1-xFexO6 (0≤x≤0.5) are reported. A structural evolution in the solid solutions from a double perovskite to perovskite is observed with increasing Fe/Re disorder. Except for the metallic parent compound all members of the series are semiconducting. For the Fe-doped samples a change from ferrimagnetic interactions in the parent compound to a complex superposition of ferrimagnetic and antiferromagnetic interactions was observed. The magnetic moment decreases with x, whereas the Curie temperature TC remains unaffected. The magnetic and Mössbauer data suggest Fe to act as a redox-buffer.