In the paragraph following eq 28, the average bond valence was incorrectly referred to as V/R. It has been corrected to V/N. The paper originally posted to the web on September 3, 2009, and was reposted on September 24, 2009.

http://pubs.acs.org/doi/pdf/10.1021/cr900053k

Recent developments in the methods and applications of the bond valence model.

A2B′B″O6 perovskites: A review

Nonlinear Optical Crystals: A Complete Survey

The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-007233.pdf

First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method

The Feature Article [1] describes the current state of the Atomic Layer Deposition (ALD) technique for producing high-quality thin layers with the focus on oxide materials such as ZrO2 and other rare earth oxides, SnO2 and ZnO for high-k dielectrics, gas sensors and various optoelectronic applications.



The cover picture is a photograph of a thin-film-on-silicon sample. The inset schematically illustrates the ALD growth of an oxide film on a surface where L refers to the precursor ligand.



The first author, Lauri Niinisto, is Professor of Inorganic Chemistry at Helsinki University of Technology. His current research is focused on the preparation and characterization of thin films for optoelectronic and electronic devices.

Advanced electronic and optoelectronic materials by Atomic Layer Deposition: An overview with special emphasis on recent progress in processing of high-k dielectrics and other oxide materials

Nonlinear optical properties of borate crystals

Optical properties of bismuth borate glasses

The dielectric constants of rare-earth oxides (RE2O3) and rare-earth nitrides, phos- phides, arsenides, and antimonides (REX, RE = rare-earth element, X = N, P, As, Sb) are quantitatively estimated. The estimation is based on the approximately linear relationship between the dielectric constant and the atomic number of the constituent atoms. Similar correlations are valid in nearly all series of related compounds; thus the approach presented here can be used as an effective tool in the search for materials with specific properties, e.g. high dielectric constants.

https://iopscience.iop.org/article/10.1088/0953-8984/12/13/319/pdf

Dielectric constants of binary rare-earth compounds

Using electron paramagnetic resonance two types of ${\mathrm{Ti}}^{3+}$-related centers are identified in BaTi${\mathrm{O}}_{3}$, which are attributed to ${\mathrm{Ti}}^{3+}$-${V}_{\mathrm{O}}$ and to ${\mathrm{Ti}}^{3+}$-${V}_{\mathrm{O}}$ associated with Na or K, respectively. This assignment is based on the chemical and illumination conditions leading to the detection of the defects. It is furthermore supported by the Ti hyperfine structure, resolved for ${\mathrm{Ti}}^{3+}$-${V}_{\mathrm{O}}$-Na(K). The symmetry of the centers is broken in the sense that an electron is localized near one of the two equivalent ${\mathrm{Ti}}^{4+}$ ions next to ${V}_{\mathrm{O}}$. Also the observed Ti hyperfine structure points to electron capture at one Ti site. The ${V}_{\mathrm{O}}$-type centers are contrasted to isolated ${\mathrm{Ti}}^{3+}$, representing a free small polaron in crystals containing ${\mathrm{Nb}}^{5+}$ and no oxygen vacancies. The participation of the ${V}_{\mathrm{O}}$ centers in photochromic processes in BaTi${\mathrm{O}}_{3}$ is studied. In crystals doped with Na or K an optical absorption precursor of the fundamental absorption is identified and attributed to the creation of an exciton bound to the ${V}_{\mathrm{O}}$-Na(K) complex.

Oxygen vacancies in BaTiO3.

A comprehensive study of conduction polarons in purified BaTiO 3 crystals, containing about 100-ppm Nb as extrinsic ions, is presented. Nb 5 + is compensated by Ti 3 + (3d 1 ) ions, many of them isolated. Small Ti 3 + polarons, stabilized by crystal strains, and polarons of intermediate size in less strained crystal regions are identified. Both species break the point symmetry, indicating stabilization by a tetragonal T 2 ×e Jahn-Teller distortion. There is indirect evidence for the presence of bipolarons in the crystal ground state. They have a rather small dissociation energy, 0.01 eV. The investigations are based on electron paramagnetic resonance (EPR) performed at T<20 K under application of uniaxial stress. This allows to obtain local information on the intrinsic Jahn-Teller properties of the conduction states of an oxide perovskite. For the small polarons stress has the following effects: (i) aligns the tetragonal Jahn-Teller axes along the stress direction, and (ii) enlarges the radius of the aligned orbitals, transforming them into intermediate ones. The stress alignment of the intermediate polarons is different: The Jahn-Teller axes orient perpendicular to the stress axis. Several of the polaron features are elucidated by comparison with the stress-dependent Jahn-Teller properties of the impurity ion Mo 5 + (4d 1 ), where the d electron is prevented from tunneling to its Ti 4 + neighbors. The EPR of Ti 3 + in reduced BaTiO 3 is attributed to polarons bound to doubly filled oxygen vacancies.

H. Hesse

Papers

Nonlinear optical properties of borate crystals

Optical properties of bismuth borate glasses

Dielectric constants of binary rare-earth compounds

Oxygen vacancies in BaTiO3.

Conduction states in oxide perovskites: Three manifestations of Ti 3+ Jahn-Teller polarons in barium titanate