The stabilities of different kinds of ordered structure in complex perovskites have been studied by the eight-point cluster variation method (CVM). The grand potentials of these structures have been calculated and compared with that of the disordered state. It has been proved that the 1/2{111}-type ordered structure will be stable in the system when the nearest-neighbour interaction is much stronger than other longer-distance interactions. The 1/2{110}- and 1/2{100}-type ordered structures result from the next-nearest- and the third-neighbour interactions respectively. The grand potentials of the 1/2{111}- and 1/2{100}-type ordered structures reach minima at the composition x = 0.5, whereas the grand potential of one of the 1/2{110}-type ordered structures reaches its minima at around x = 0.25 and x = 0.75. The formation of different kinds of ordered structure in real material systems has been discussed.

Gui Hong;Zhang Xiaowen;Gu Binglin

Journal of Physics Condensed Matter

1996

Recent Moessbauer isomer shift measurements on **1**1**9Sn impurities implanted in A**I**I**IB**V compounds are interpreted in terms of the band structure of the host crystal and the electronic structure of the implanted Sn atoms/ions. A Green-function perturbation procedure based on the tight-binding method is used to determine the internal electronic configuration of ionized Sn donors and acceptors, and to calculate the relevant isomer shifts. It turns out that with the Sn acceptors the impurity is formed by a small cluster containing the tin atom in its neutral configuration rather than by a single negative Sn ion as might be anticipated at first sight. On the other hand, in the donor case the positive Sn ion plays the dominant role.

Antoncik E.;Gu B. L.

Physica B Physics of Condensed Matter C Atomic Molecular and Plasma Physics Optics

1982

The Moessbauer isomer shift provides a unique technique for studying the electronic structure of solids on the atomic scale and in many cases makes it possible to check the accuracy of the wave functions resulting from either the band-structure calculations or the solution of the impurity problem. Using a Green-function procedure based on a modified tight-binding method, the electronic configuration and the relevant isomer-shift values have been evaluated for several physically interesting cases. In particular, **1**1**9Sn, **1**2**1Sb, and **1**2**5Te, representing either one of the components or an impurity in various A**NB**8** minus **N semiconducting materials, are considered, and their local structure is discussed in detail.

Antoncik Emil;Gu Bing lin

Physica B Physics of Condensed Matter C Atomic Molecular and Plasma Physics Optics

1982

The YBa 2 Cu 3 O 7-x undergoes order-disorder phase transitions between orthorhombic and tetragonal structure. This transition modifies both the long-range and short-range order order of the CuO plane as a function of composition (7-x). This affects thermodynamic quantities such as the order parameter, entropy, and phase diagram as well as lattice parameters. These quantities are calculated with the Kikuchi approximation. The results are in good agreement with experiment. © 1988.

Gu Bing-Lin;Wang Qiang;Zhang Xiao-Wen

Physica C Superconductivity and Its Applications

1988

Under the bound-state approximation, subbands of electrons and holes in GaAs/GaAlAs quantum wells with different shapes in an electric field are solved by using the method of series expansion. A variational method is used to obtain the binding energies of excitons. Based on these, we have obtained the variational picture of the energy shifts of subbands and excitons from a parabolic to a square well. Considering the effect of the shape of GaAs/GaAlAs quantum well, the calculated results agree with experiments.

Zhu Jialin;Tang Daohua;Gu Binglin;Xiong Jiajiong

Pan Tao Ti Hsueh Pao Chinese Journal of Semiconductors

1989

The oxygen ordering in the CuO plane of YBa2Cu3O7-y is investigated by introducing three-body interaction (TBI) based on the two-dimensional Ising model with the asymmetric next nearest neighbor interaction. The correlation of two neighbor CuO chains is discussed and phase diagrams are calculated by application of the cluster variation method ( CVM ). The double-cell structure at high temperature can be stabilized by the TBI. The average of the pair probabilities along the CuO chains shows a smooth plateau in the range of 0.3 < y < 0.53, and is similar to the dependence of Tc and room temperature resistivity on oxygen content. © 1989.

Wang Ming-liang;Gu Bing-lin

Physica C Superconductivity and Its Applications

1989

Based on a generalized Ising model in which first-, second- and third-neighbor interaction are considered and a combinative cluster variation method of a five- and a four-body square cluster is utilized, the structural transitions are discussed and a phase diagram is obtained. The calculation results show that the third-neighbor interactiom contributes to the existence of the double cell structure at relative high temperature, and are in good agreement with recent experimental observations. © 1989.

Gu Bing-Lin;Wang Ming-Liang;Duan Wen-hui;Wang Qiang;Zhang Xiao-Wen

Physica C Superconductivity and Its Applications

1989

Ultrasonic measurement revealed that there are anomalous structural changes near 200 K in single 2212 or 2223 phase samples of Bi(Pb)SrCaCuO. Detailed study showed such anomalous changes are isothermal-like processes and have a characteristics of second order phase transition,accompanying with increase in lattice constants. The elastic properties of these ceramics and related systems are also discussed. © 1989.

He Y. S.;Xiang J.;Chang F. G.;Zhang J. C.;He A. S.;Wang H.;Gu B. L.

Physica C Superconductivity and Its Applications

1989

Yttria-Stabilized Zinconia (YSZ) and YBa2Cu3O7-δ were ablated sequentially by a XeCl ecximer laser and deposited on Si(100) substrate heated to temperature of 650°C to in-situ fabricate high Te superconducting YBCO/YSZ/Si thin films. The zero resistance temperature of the deposited film was measured to be 85K by four-point method. The X-ray diffraction pattern of the film shows that it has strong c-axis orientation normal to the film surface. RBS and AES profile analysis were used to determine the chemical composition, thickness and interfaces of the multilayers. © 1991.

Zhang Yaogang;Fan Shoushan;Shi Changqing;Niu Zhichuan;Gu Binglin

Physica C Superconductivity and Its Applications

1991

The phase diagram and metastable phase diagram are calculated based on an improved model for the structure of the alloy (GaAs)1-xSi2x. The modified Kikuchi approximation is used with the interaction energies of the nearest-neighbor atom pairs calculated by the universal parameter tight-binding method. There is a metastable order-disorder transition point for the alloy (GaAs)1-xSi2x at xc = 0.26 which is consistent with the experiment. The band gaps of the alloy are also calculated. © 1992.

Ni Jun;Gu Binglin

Solid State Communications

1992