ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06428.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06429.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The first‐principles orthogonalized linear combination of atomic orbitals (OLCAO) method for electronic structure studies has been applied to a variety of complex inorganic crystals. The theory and the practice of the OLCAO method in the local density approximation are discussed in detail. Recent progress in the study of electronic and optical properties of a large list of ceramic systems are summarized. Eight selected topics on different ceramic crystals focusing on specific points of interest are presented as examples. The materials discussed are AIN, Cu2O, β‐Si3N4, Y2O3, LiB3O5, ferroelectric crystals, Fe‐B compounds, and the YBa2Cu3O7superconductor. The results include the band structure, density of states, charge density distribution, spin density distribution, effective charges, total energy and totalenergy‐derived results, optical absorption, positron annihilation spectra, and more. Extension of the band theoretical approach to the study of other areas of fundamental ceramic science is also d

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06430.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Photoemission spectroscopy has recently emerged as one of the leading techniques in the study of high‐temperature superconductors. Relevant successes include the direct detection of the superconductivity gap, tests for departure from Fermi‐liquid behavior, and many interface chemical studies with technological interest. We present a review of the fundamental and applied aspects of this technique; the review is written for readers who are not specialized in electron spectroscopy or surface scie

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06431.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The ab initio pseudofunction method has been used to compute electronic properties of superconductors in good agreement with experiment. La2CuO4and CuO are computed to be antiferromagnetic and semiconducting in agreement with experiment. The 0.4‐eV peak in the optical conductivity spectrum has been shown to be an interband transition for YBa2Cu3O7. The bands for Bi2Sr2CaCu2O8as well as YBa2Cu3O7agree well with angle‐resolved photoemission nearEf. The shake‐up peaks near 9 and 12 eV observed in photoemissio can be understood in terms of two‐electron processes envolving the local densities of states of Cu and O. A mechanism for superconductivity based on these electronic properties will be advanced. All calculations use local density potentials with no par

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06432.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Atomistic lattice simulations are reported of the normalstate crystal properties of high‐Tcoxides. Nonstoichiometry in La2CuO4and Nd2CuO4associated with oxygen interstitial defects is examined in some detail. The lattice structure and defect chemistry of Ca2CuO3, Sr2CuO3, La2SrCu2O6, and Sr2CuO4are also considered. Finally, Jahn‐Teller effects and bipolaron formation are addressed in relation to high‐Tcbeh

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06433.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Simulation techniques are applied to the orthorhombic YBa2Cu3O7crystal in order to describe possible polaron and bipolaron species in the crystal. Perfect crystal properties are fitted well with a two‐ and three‐body potential model. The O−polaron state is significantly stabilized by the presence of holes in the CuO plane. A bipolaron O2−2is slightly stable on the O4and O2or O3lattice ion sites of oxygen. The oxidation reaction leading to O−and involving Cu+and oxygen vacancies is e

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06434.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A technique for measuring stress (positive and negative) with a lateral spatial extent of approximately 2 μm is introduced. The technique, implemented using a Raman microprobe, is demonstrated with measurements of the frequency shift of the sharp, R‐luminescence lines (2Ā and Ē to4A2radiative transitions) in, and around, a hardness indentation in a 0.06‐wt%‐chromium doped sapphire. From the observed frequency shifts the stresses in regions sampled in the hardness impression, in the complex stress field surrounding it, and at the tip of a crack are

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06435.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The effects of high temperature on the electronic structure of a material consist of two major contributions, thermal lattice expansion and the electron‐phonon interaction. These can produce dramatic changes in the electronic structure and play a critical role in the high‐temperature properties and behavior of ceramics. We have used ab initio pseudofunction band structure methods to calculate the temperature dependence of the electronic structure of MgO from 300 to 1300 K modeling the independent effects of thermal lattice expansion and the electron‐phonon interaction. The band structure calculations were performed self‐consistently on a (MgO)4supercell using experimental values obtained from high‐temperature X‐ray diffraction to determine the lattice constants up to 1300 K and the root mean square amplitude of phonon displacements. Lattice thermal expansion contributed ‐0.15 meV/K to the band gap temperature dependence. Individual phonon modes, with displacements in the 〈111〉, 〈110〉, and 〈100〉 directions, were modeled using distorted lattice calculations. The electron‐phonon coupling was found to be strongest for the 〈100〉 mode modeled, with strong coupling seen for modes which lead to the smallest decrease in the Mg‐O bond length. The overall magnitude of the electron‐phonon contribution to the band gap temperature dependence for the phonon modes modeled was −0.95 meV/K. The theoretical results account for a band gap temperature dependence in MgO of −1.1 meV/K, which compares well with the temperature dependence of approximately −1 meV/K determined experimenta

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06436.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Barium titanate (BaTiO3) is an important electrooptic ferroelectric oxide material which exhibits the unusual optical nonlinearity of photorefractivity. There is evidence that the photorefractive effect, which refers to the change in the index of refraction of the crystal by the action of light, is related to the presence of defects/impurities such as transition metal ions and/or cation or anion vacancies. This paper will review our electron paramagnetic resonance, optical, and theoretical eletronic structure studies aimed at probing the nature of the defects/impurities in BaTiO3and their role in the photorefractive effect.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1990.tb06437.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY