材料期刊网

SYNTHESIS OF ULTRAFINE PLZT POWDER BY A SIMPLE CO- PRECIPITATION METHOD

H. Ying1) , X. D. Sun1) , Q. B. Yang1) , J. B. Li2) , Y. M. Wang2) , Z. Zhang3) and J. You3)1) School of Materials and Metallurgy , Northeastern University , Shenyang 110006 , China2) Departm ent of Materials , School of Mechanical Engineering , Shenyang University , Shenyang110044 , China3) Liaoning Analyzing and Testing Research Center , Shenyang 110015 , China

金属学报(英文版)

Starting from cheap inorganic salts , ultrafine P L Z T po w ders were synthesized by a co pre cipitation m ethod . The results show that the precursor precipitate obtained by the co precipita tion method transfor ms co m pletely to P L Z T phase by calcining at 420 ℃ for 4 hours , about300 ℃low er than the nor m al transform ation te m perature of P L Z T obtained by m ixed oxidemethod . The effect of residual N H4 N O3 in the precursor precipitate on transfor m ation te m perature of the P L Z Tpow der w as investigated . The residual N H4 N O3 in the precursor po w der can reduce further the P L Z Ttransfor m ation tem perature to about 300 ℃, but a sm alla mount of Zr O2 and Pb Ti O3 re m ained . By a proper control of the synthesizing route , a P L Z T po w der with a pri m ary particle size of 10 n m and an agglom eration size of 0 3 μm hasbeen produced .

关键词: P L Z T , null , null

Theoretical studies on the off-center displacement of Ni3+ in SrO by analyzing its anisotropic g factors

Journal of Alloys and Compounds

The off-center displacement of Ni3+ ion in SrO crystal is investigated by analyzing its anisotropic g factors g(//) and g(perpendicular to) by using the perturbation formulas of the g factors for a 3d(7) ion in axial (tetragonal or trigonal) symmetry. In these formulas, the contributions to the g factors from the mixture of different energy states, low symmetry distortion and covalency effect are included and the parameters related to these effects can be obtained from the optical spectral and local structural parameters of the studied system. Based on the studies, it is found that the Ni3+ impurity may take an off-center displacement by about 0.23 Angstrom along the [1 1 1] direction and result in a trigonally distorted [NiO6](9-) cluster. Interestingly, the observed Ni3+ center has the unusual T-4(1) ground orbital triplet due to the weak crystal field of the host SrO, which is different from the usual E-2 ground orbital doublet for Ni3+ under strong octahedral fields. The reasonableness of the results is discussed. (C) 2003 Elsevier B.V. All rights reserved.

关键词: defect structure;electron paramagnetic resonance;crystal- and;ligand-field theory;Ni3+;SrO;atomic screening constants;transition metal ions;paramagnetic-resonance;spin resonance;superposition model;scf;functions;crystals;oxide;co2+;epr

Introduction to atmospheric corrosion research in China

Science and Technology of Advanced Materials

In this paper, we introduce the research on atmospheric corrosion in China. We describe the climate characteristics and the classification of atmospheric corrosivity across the whole country. We also describe the rusting evolution under simulated wet/dry cyclic conditions. (C) 2007 NIMS and Elsevier Ltd. All rights reserved.

关键词: atmospheric corrosion;corrosivity;rusting evolution;weathering steels;rust;mechanism;so2;o-3;no2

Recent developments in high temperature intermetallics research in China

Intermetallics

A comprehensive survey was made of various advances of intermetallics research in China. The investigation focussed on the fundamental research and materials development. Charge density distribution and site occupancy of alloying elements, environmental embrittlement and chemical reaction, interface structures and phase transformation at the atomic scale, nanocrystalline intermetallics and its thermal stability, superplastic behavior and anomalous yield strength peak are reviewed. Several Ti-Al and Ni-Al based alloys have been manufactured, and show good mechanical properties. Diverse components have been fabricated successfully. (C) 2000 Elsevier Science Ltd. All rights reserved.

关键词: aluminides, miscellaneous;hydrogen embrittlement;mechanical properties;at high temperatures;superplastic behavior;phase interfaces;grain-boundary fracture;in-situ composites;environmental;embrittlement;hydrogen embrittlement;ni3al;compression;alloys;co3ti;boron;feal

Defect structure of the tetragonal Cu2+ center in PbTiO3 : Cu2+ crystal

Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences

defect structure of the tetragonal Cu2+ center in PbTiO3: Cu2+ crystal is studied by analyzing the EPR g factors and hyperfine structure constants. From the study, we suggest that an oxygen vacancy occurs in the nearest-neighbors site of Cu2+ due to charge compensation, and that the off center displacement of Cu2+ is smaller than that of the replaced host ion Ti4+. The reasonableness of the defect structure is discussed.

关键词: defect structure;electron paramagnetic resonance;crystal-field theory;Cu2+;PbTiO3;electron-paramagnetic-resonance;superposition model;single-crystals;batio3;ions;ni

Defect structure of Co2+ center in rhombohedral BaTiO3

Optical Materials

The spin-Hamiltonian parameters (g factor g(parallel to), gi(perpendicular to) and hyperfine structure constants A(parallel to), A(perpendicular to)) of Co2+ ion in rhombohedral BaTiO3 crystal are calculated from the perturbation formulas based on the cluster approach for the spin-Hamiltonian parameters of 3d(7) ion in trigonal octahedral site. The calculations are related to the trigonal field parameters and hence to the defect structure of Co2+ center. From the calculations, it is found that in order to reach a good fit between calculations and experiments, the off-center displacement of Co2+ ion in oxygen octahedron of BaTiO3 is much smaller than that of the host Ti4+ ion it replaces. This point is similar to the case of Fe3+ ion in BaTiO3 obtained in the previous studies by analyzing EPR zero-field splitting from the superposition model. (c) 2005 Elsevier B.V. All rights reserved.

关键词: defect structure;electron paramagnetic resonance;crystal and ligand;field;photorefractive material;Co2+;BaTiO3;electron-paramagnetic-resonance;atomic screening constants;photorefractive properties;superposition model;scf functions;dependence;position;distance;fields;sites

Studies on the local structure of the tetragonal Er3+ center in CaO

Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences

The local structure of the tetragonal Er3+ center in CaO is theoretically studied by using the perturbation formulas of the g factors for a 4f(11) ion in tetragonal symmetry. In these formulas, the contributions to the g factors from the second-order perturbation terms and the admixtures of various states are taken into account. Based on the investigations, this center is suggested to be the impurity Er3+ substituting the host Ca2+ site, associated with a Ca2+ vacancy V-Ca in the [100] (C-4) axis due to charge compensation. By studying the g factors of the tetragonal center, impurity Er3+ is expected to undergo an off-center displacement Delta Z( approximate to 0.2 A) towards the V-Ca along the C-4 axis because of the electrostatic attraction. The calculated g factors based on the displacement Delta Z show reasonable agreement with the observed values.

关键词: defect structures;electron paramagnetic resonance (EPR);crystal-field;and spin hamiltonians;Er3+;CaO;electron-spin-resonance;superposition-model;insulator coatings;magnesium-oxide;vanadium alloys;single-crystals;calcium oxide;parameters;blankets;ions

R&D STATUS ON INTERMETALLICS IN CHINA

CHEN Guoliang(State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 , China)SHI Changxu (Academia Sinica , Beijing 100864 , China)

金属学报(英文版)

This paper briefiy introduces the R&D of intermetallics in China. R&D on intermetallics in a national scale in China began near ten years ago. The investigation in past years focused on the fundamental research and materials development. A significant progress has been made. Various components that made of Ti3Al Ni3Al, TiAl and Fe3Al have been successfully manufactured Some of them have been evaluted. It is expected that some intermetallic alloys will be produced in an industrial scale in the near future.

关键词: :intermetallic alloys , null , null , null

Spin-Hamiltonian parameters and off-center displacements for Rh4+and Ir4+ions in rhombohedral BaTiO3

Radiation Effects and Defects in Solids

By means of the formulae based on the first-order theory of resonance for a low-spin 2T2 term in trigonal symmetry, the spin-Hamiltonian parameters (g factors g//, g and hyperfine structure constants A//, A) for Rh4+(4d5) and Ir4+(5d5) ions in the low-temperature rhombohedral phase of BaTiO3 are calculated. The calculated results are in reasonable agreement with the experimental values. From the calculations, the off-center displacements of Rh4+ and Ir4+ in the oxygen octahedra of BaTiO3 crystal are acquired. These impurity displacements are much smaller than that of the replaced host ion Ti4+. This point is analogous to the displacements of 3dn impurities Fe3+ and Co2+ in rhombohedral BaTiO3 obtained by analyzing their spin-Hamiltonian parameters.

关键词: defect structure;EPR spectra;crystal- and ligand-field theory;BaTiO3;Ru4+;Ir4+;electron-paramagnetic-resonance;yttrium gallium garnet;orthophosphate;mpo4 m;optical-absorption;defect structure;local-structure;y;crystals;fe3+ ions;epr;position

Theoretical investigations of the defect structure and the g factors of a tetragonal Ni3+ center in PbTiO3

Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences

The defect structure and the anisotropic g factors of a tetragonal Ni3+ center in PbTiO3 are theoretically investigated from improved perturbation formulas of the g factors for a 3d(7) ion with low spin S = 1/2 in tetragonally elongated octahedra, established in this work. Based on the studies, the distance between the impurity Ni3+ and the center of the oxygen octahedron is found to be about 0.14 A, which is smaller than that (approximate to 0.3 angstrom) for the host Ti4+ site due to the inward shift (approximate to 0.16 angstrom) towards the center of the oxygen octahedron. The theoretical g factors based on the above defect structure agree well with the observed values.

关键词: defect structures;electron paramagnetic resonance;crystal-fields and;spin Hamiltonian;Ni3+;PbTiO3;electron-paramagnetic-resonance;atomic screening constants;superposition model;epr parameters;lead titanate;scf functions;ions;crystals;cr3+;nanopowders