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First Principles Studies on the Electronic Structure and Band Structure of Paraelectric SrTiO3 by Different Approximations  [PDF]
H. Salehi
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.29111
Abstract: The electronic structure, energy band structure, total density of states (DOS) and electronic density of perovskite SrTiO3 in the cubic phase are calculated by the using full potential-linearized augmented plane wave (FP-LAPW) method in the framework density functional theory (DFT) with the generalized gradient approximation (GGA) by WIEN2k package. The calculated band structure shows a direct band gap of 2.5 eV at the Γ point in the Brillouin zone.The total DOS is compared with experimental x-ray photoemission spectra. From the DOS analysis, as well as charge-density studies, I have conclude that the bonding between Sr and TiO2 is mainly ionic and that the TiO2 entities bond covalently.The calculated band structure and density of state of SrTiO3 are in good agreement with theoretical and experimental results.
First-principles study of La and Sb-doping effects onelectronic structure and optical properties of SrTiO3

Yun Jiang-Ni,Zhang Zhi-Yong,Yan Jun-Feng,Deng Zhou-Hu,

中国物理 B , 2010,
Abstract: The effects of La and Sb doping on the electronic structure and optical properties of SrTiO3 are investigated by first-principles calculation of the plane wave ultra-soft pseudo-potential based on density functional theory. The calculated results reveal that corner-shared TiO6 octahedra dominate the main electronic properties of SrTiO3, and its structural stability can be improved by La doping. The La3+ ion fully acts as an electron donor in Sr0.875La0.125TiO3 and the Fermi level shifts into the conduction bands (CBs) after La doping. As for SrSb0.125Ti0.875O3, there is a distortion near the bottom of the CBs for SrSb0.125Ti0.875O3 after Sb doping and an incipient localization of some of the doped electrons trapped in the Ti site, making it impossible to describe the evolution of the density of states (DOS) within the rigid band model. At the same time, the DOSs of the two electron-doped systems shift towards low energies and the optical band gaps are broadened by about 0.4 and 0.6 eV for Sr_0.875La_0.125TiO3 and SrSb0.125Ti0.875O3, respectively. Moreover, the transmittance of SrSb0.125Ti0.875O3 is as high as 95\% in most of the visible region, which is higher than that of Sr0.875La0.125TiO_3 (85\%). The wide band gap, the small transition probability and the weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the significant optical transparency of SrSb_0.125Ti_0.875O3.
Atomic-scale structure of the SrTiO3(001)-c(6x2) reconstruction: Experiments and first-principles calculations  [PDF]
C. H. Lanier,A. van de Walle,N. Erdman,E. Landree,O. Warschkow,A. Kazimirov,K. R. Poeppelmeier,J. Zegenhagen,M. Asta,L. D. Marks
Physics , 2007, DOI: 10.1103/PhysRevB.76.045421
Abstract: The c(6x2) is a reconstruction of the SrTiO3(001) surface that is formed between 1050-1100oC in oxidizing annealing conditions. This work proposes a model for the atomic structure for the c(6x2) obtained through a combination of results from transmission electron diffraction, surface x-ray diffraction, direct methods analysis, computational combinational screening, and density functional theory. As it is formed at high temperatures, the surface is complex and can be described as a short-range ordered phase featuring microscopic domains composed of four main structural motifs. Additionally, non-periodic TiO2 units are present on the surface. Simulated scanning tunneling microscopy images based on the electronic structure calculations are consistent with experimental images.
Influence of rotational instability on the polarization structure of SrTiO3  [PDF]
Yanpeng Yao,Huaxiang Fu
Physics , 2010, DOI: 10.1103/PhysRevB.82.174119
Abstract: The k-space polarization structure and its strain response in SrTiO3 with rotational instability are studied using a combination of first-principles density functional calculations, modern theory of polarization, and analytic Wannier-function formulation. (1) As one outcome of this study, we rigorously prove-both numerically and analytically-that folding effect exists in polarization structure. (2) After eliminating the folding effect, we find that the polarization structure for SrTiO3 with rotational instability is still considerably different from that for non-rotational SrTiO3, revealing that polarization structure is sensitive to structure distortion of oxygen-octahedra rotation and promises to be an effective tool for studying material properties. (3) Furthermore, from polarization structure we determine the microscopic Wannier-function interactions in SrTiO3. These interactions are found to vary significantly with and without oxygen-octahedra rotation.
First principles study of CaTiO3 crystal in paraelectric and ferroelectric phases  [cached]
S. H. Hashemi,A. Kompany,S. M. Hosseini
Iranian Journal of Physics Research , 2005,
Abstract: Electronic properties of CaTiO3 crystal in paraelectric and ferroelectric phases have been studied by first principles, using Hohenberg-Kohn-Sham density functional theory (DFT). In paraelectric phase the results show an indirect band gap of about 2eV at -R direction in the Brilluoin zone and a strong hybridization between Ti-3d an O-2P orbital. In ferroelectric phase a direct band gap of about 1eV is seen at point. Up to our knowledge no data has been reported on the ferroelectric phase so far, therefore our results might be useful for the future works.
First-principles study of symmetry lowering in relaxed BaTiO3/SrTiO3 superlattices  [PDF]
Karen Johnston,Xiangyang Huang,Jeffrey B. Neaton,Karin M. Rabe
Physics , 2004, DOI: 10.1103/PhysRevB.71.100103
Abstract: The crystal structure and local spontaneous polarization of (BaTiO3)m/(SrTiO3)n superlattices is calculated using a first-principles density functional theory method. The in-plane lattice constant is 1% larger than the SrTiO3 substrate to imitate the relaxed superlattice structure and the symmetry is lowered to monoclinic space group Cm which allows polarization to develop along the [110] and [001] directions. The polarization component in the [110] direction is found to develop only in the SrTiO3 layers and falls to zero in the BaTiO3 layers, whereas the polarization in the [001] direction is approximately uniform throughout the superlattice. These findings are consistent with recent experimental data and first-principles results for epitaxially strained BT and ST.
Impurity-induced Polar States in SrTiO3 Quantum Paraelectric  [PDF]
P. A. Markovin,V. A. Trepakov,M. E. Guzhva,A. G. Razdobarin,A. K. Tagantsev,D. A. Andreev,M. Itoh,A. Dejneka
Physics , 2015,
Abstract: Short and long range impurity-induced polar ordering in Sr1-xCaxTiO3 with x = 0.014 (SCT-1.4) and SrTi(16O0.0318O0.97)3 (STO-18) single crystals were investigated and discussed on the basis of the light refraction temperature dependences measurements. For SCT-1.4 the temperature dependences of the morphic birefringence and dielectric hysteresis loops were measured. Within the optical indicatrix perturbation approach a method for calculation from polar contributions to the refraction of light of short-range polarization contribution Psh originated by spatial fluctuations is developed for the systems with the coexistence of long and short range polar ordering. The magnitudes and temperature dependences of Psh and long-range spontaneous polarization Ps have been determined in SCT-1.4 and STO-18. The results allowed to characterize quantitatively and to compare contributions of short (Psh) and long (Ps) range ordering in the formation of impurity-induced polar phase in SrTiO3.
Nanoscale Electromechanics of Paraelectric Materials with Mobile Charges: Size effects and Nonlinearity of Electromechanical Response of SrTiO3 Films  [PDF]
A. N. Morozovska,E. A. Eliseev,G. S. Svechnikov,S. V. Kalinin
Physics , 2011, DOI: 10.1103/PhysRevB.84.045402
Abstract: Nanoscale enables a broad range of electromechanical coupling mechanisms that are forbidden or negligible in the materials. We conduct a theoretical study of the electromechanical response of thin paraelectric films with mobile vacancies (or ions) paradigmatic for capacitor-type measurements in X-ray scattering, piezoresponse force microscopy (PFM), and electrochemical strain microscopy (ESM). Using quantum paraelectric SrTiO3 film as a model material with well known electromechanical, electronic and electrochemical properties, we evaluate the contributions of electrostriction, Maxwell stress, flexoelectric effect, deformation potential and compositional Vegard strains caused by mobile vacancies (or ions) and electrons to the electromechanical response. The local electromechanical response manifests strong size effects, the scale of which is determined by the ratio of the SrTiO3 film thickness and PFM/ESM tip size to the carriers screening radius. Due to the strong dielectric nonlinearity effect inherent in quantum paraelectrics, the dependence of the SrTiO3 film electromechanical response on applied voltage demonstrates a pronounced crossover from the linear to the quadratic law and then to the sub-linear law with a factor of 2/3 under the voltage increase. The temperature dependence of the electromechanical response as determined by the interplay between the dielectric susceptibility and the screening radius is non-monotonic and has a pronounced maxima, the position and width of which can be tuned by film thickness. This study provides a comparative framework for analysis of electromechanical coupling in the non-piezoelectric nanosystems.
Origin of the large phonon band-gap in SrTiO3 and the vibrational signatures of ferroelectricity in ATiO3 perovskite: First principles lattice dynamics and inelastic neutron scattering of PbTiO3, BaTiO3 and SrTiO3  [PDF]
Narayani Choudhury,E. J. Walter,A. I. Kolesnikov,C. -K. Loong
Physics , 2008, DOI: 10.1103/PhysRevB.77.134111
Abstract: We report first principles density functional perturbation theory calculations and inelastic neutron scattering measurements of the phonon density of states, dispersion relations and electromechanical response of PbTiO3, BaTiO3 and SrTiO3. The phonon density-of-states of the quantum paraelectric SrTiO3 is found to be fundamentally distinct from that of ferroelectric PbTiO3 and BaTiO3 with a large 70-90 meV phonon band-gap. The phonon dispersion and electromechanical response of PbTiO3 reveal giant anisotropies. The interplay of covalent bonding and ferroelectricity, strongly modulates the electromechanical response and give rise to spectacular signatures in the phonon spectra. The computed charge densities have been used to study the bonding in these perovskites. Distinct bonding characteristics in the ferroelectric and paraelectric phases give rise to spectacular vibrational signatures. While a large phonon band-gap in ATiO3 perovskites seems a characteristic of quantum paraelectrics, anisotropy of the phonon spectra correlates well with ferroelectric strength. These correlations between the phonon spectra and ferroelectricity, can guide future efforts at custom designing still more effective piezoelectrics for applications. These results suggest that vibrational spectroscopy can help design novel materials.
Polar Order in Quantum Paraelectric SrTiO3-16 and SrTiO3-18 at Low Temperature  [PDF]
Yoshiaki Uesu,Ryuhei Nakai,Jean-Michel Kiat,Carole Menoret,Mitsuru Itoh,Toru Kyomen
Physics , 2004, DOI: 10.1143/JPSJ.73.1139
Abstract: Optical second-harmonic generation (SHG) in SrTi16O3 (STO16) and SrTi18O3 (STO18) was investigated using the SHG microscope. While no-biased STO16 exhibits weak and almost temperature-independent SHG signals, a marked SHG is observed under the electric field in the quantum paraelectric region. In STO18, strong SHG signals appear spontaneously below 36K. However, neutron and X-ray diffraction analyses indicate that no structural change appears at low temperature in STO18, and STO16 under the electric field. By taking into account the fact that the SHG is sensitive to the local polar-order, the combined studies reveals that the long-range order of polar phase does not develop on the both crystals and is frozen in local regions.
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