Search results for "Strontium titanate"
showing 10 items of 37 documents
The electronic properties of SrTiO3-δ with oxygen vacancies or substitutions
2021
The authors would like to thank R. Dittmann for useful discussions, T. Kocourek, O. Pacherova, S. Cichon, V. Vetokhina, and P. Babor for their contributions to sample preparation and characterization. The authors (M.T., A.D.) acknowledge support from the Czech Science Foundation (Grant No. 19-09671S), the European Structural and Investment Funds and the Ministry of Education, Youth and Sports of the Czech Republic through Programme “Research, Development and Education” (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16-019/0000760). This study was partly supported by FLAG-ERA JTC project To2Dox (L.R. and E.K.). Calculations have been performed on the LASC Cluster in the Institute of Solid State Phy…
Local dynamics and phase transition in quantum paraelectric SrTiO3 studied by Ti K-edge x-ray absorption spectroscopy
2016
Strontium titanate is a model quantum paraelectric in which, in the region of dominating quantum statistics, the ferroelectric instability is inhibited due to nearly complete compensation of the harmonic contribution into ferroelectric soft mode frequency by the zero- point motion contribution. The enhancement of atomic masses by the substitution of 16 O with 18O decreases the zero-point atomic motion, and low-T ferroelectricity in SrTi18O3 is realized. In this study we report on the local structure of Ti in SrTi16O3 and SrTi18O3 investigated by Extended X-ray Absorption Fine Structure measurements in the temperature range 6 - 300 K.
Energetic stability and photocatalytic activity of SrTiO3 nanowires: ab initio simulations
2015
First principles periodic calculations based on the density functional theory within the localized atomic orbital approach (DFT-LCAO) using the hybrid exchange–correlation potential PBE0 have been performed in order to simulate the structural and electronic properties of both stoichiometric and nonstoichiometric [001]-oriented four-faceted SrTiO3 (STO) nanowires (NW) of cubic structure. Their diameters have been varied from 0.3 up to 2.4 nm with a corresponding consequent change of NW cross-section from 2 � 2t o 5� 5 extension of the lattice constant in bulk. Energetic stability of STO NW (both stoichiometric and non-stoichiometric) has been found to increase with the decrease of their form…
Enhanced thermoelectric properties of lightly Nb doped SrTiO3 thin films
2021
Novel thermoelectric materials developed for operation at room temperature must have similar or better performance along with being as ecofriendly as those commercially used, e.g., BiTe, in terms of their toxicity and cost. In this work, we present an in-depth study of the thermoelectric properties of epitaxial Nb-doped strontium titanate (SrTiNbO) thin films as a function of (i) doping concentration, (ii) film thickness and (iii) substrate type. The excellent crystal quality was confirmed by high resolution transmission electron microscopy and X-ray diffraction analysis. The thermoelectric properties were measured by the three-omega method (thermal conductivity) and van der Pauw method (el…
Dielectric relaxation of space charges and polarons in ferroelectric perovskites
2001
Abstract In all ferroelectric perovskites, intentionally introduced or “unwanted” point defects do play a role in the dielectric spectra and in the conductivity. Above room temperature, space charge relaxation at the electrodes interfaces are observed. This can be of interest in the context of the nowadays applications of ferroelectric thin films. At liquid helium temperatures much more localised dielectric relaxation occurs. Special emphasis will be brought on SrTiO3 which has received renewed interest at the beginning of the nineties and for which a wealth of reliable experimental data are available. Considering that a gradual freezing of polarized objects is occurring at low temperatures…
Comparative study of polar perovskite surfaces
2004
A novel model of the ‘‘zig–zag’’ (1 1 0) polar surface termination of ABO3 perovskites is suggested and analyzed. Classical shell model calculations for BaTiO3, SrTiO3 and LaMnO3 show that such the (1 · 2) (1 1 0) surface reconstruction has the lowest energy, comparable to that for the (1 0 0) surfaces. The calculated surface energy reaches the saturation only when 6–8 atomic near-surface planes are allowed to relax. Surface relaxation leads to the formation of considerable dipole moment perpendicular to the surface. The predicted surface polarization of thin perovskite films, even in the cubic phase, could affect their dielectric properties. � 2004 Elsevier B.V. All rights reserved.
Ab initio study of the SrTiO3, BaTiO3 and PbTiO3 (001) surfaces
2004
The results of first-principles calculations of the two possible terminations of (0 0 1) surfaces of SrTiO 3 (STO), BaTiO3 (BTO) and PbTiO3 (PTO) perovskites are presented. Surface atomic structures and their electronic configurations have been calculated using ab initio density functional theory (DFT) combined with hybrid (B3PW) exchange-correlation technique. Our results are compared with previous quantum mechanical calculations and available experimental data. Surface relaxations and the electronic states near valence band gap are discussed in details for all three perovskites. © 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Hybrid DFT calculations of the atomic and electronic structure for ABO3 perovskite (001) surfaces
2005
Abstract We present the results of first-principles calculations on two possible terminations of the (0 0 1) surfaces of SrTiO3, BaTiO3, and PbTiO3 perovskite crystals. Atomic structure and the electronic configurations were calculated for different 2D slabs, both stoichiometric and non-stoichiometric, using hybrid (B3PW) exchange-correlation technique and re-optimized basis sets of atomic (Gaussian) orbitals. Results are compared with previous calculations and available experimental data. The electronic density distribution near the surface and covalency effects are discussed in details for all three perovskites. Both SrTiO3 and BaTiO3 (0 0 1) surfaces demonstrate reduction of the optical …
Probing Nanoscale Ferroelectricity by Ultraviolet Raman Spectroscopy
2006
We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature ( T c ) in ferroelectric ultrathin films and superlattices. We showed that one-unit-cell-thick BaTiO 3 layers in BaTiO 3 /SrTiO 3 superlattices are not only ferroelectric (with T c as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO 3 layers adjacent to them. T c was tuned by ∼500 kelvin by varying the thicknesses of the BaTiO 3 and SrTiO 3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.
Relaxation of electronic excitations in strontium titanate
2002
The transient absorption spectra and kinetics were studied for undoped, lead doped and high purity SrTiO 3 single crystals. The pulsed electron beam induced transient absorption is studied in all crystals. The strong absorption at 0.8 v eV was observed only in high purity SrTiO 3 . This absorption is suggested to arise from intrinsic electron polaron. The bound electron polarons are likely responsible for absorption band at 1.4 v eV. The main luminescence band under excitation pulse is observed at 2.75 v eV. The luminescence decay is faster than that of transient absorption.