Single atomic lithium in solid hydrogen was simulated using the path integral Monte Carlo (PIMC) method. Effects of pressure on the trapping site structures and absorption spectra of Li in both pure solid H2and doped solid were studied. The studies were done at zero pressure and at pressure range of 0-4.8 GPa. It was found for zero pressure that a large partition number was needed to calculate very accurate energetic results for pure solid hydrogen. While the energies for pure solid hydrogen and the doped solid increased with increasing pressure. Pressure detects the properties which cannot be observed at zero pressure due to weak interaction.

Ma Y. M.;Cui T.;Zou G. T.

Journal of Chemical Physics

2001

A dielectric constant measurement was carried out on perovskite-type ferroelectrics KNbO3 over a wide range of temperature under high pressure. The temperature- and pressure-dependence of the dielectric constant clarified that all temperatures of the transitions from the ferroelectric rhombohedral to orthorhombic, to tetragonal and then to the paraelectric cubic phase, decrease with increasing pressure. These results indicate that the orthorhombic-tetragonal transition takes place at 8.5 GPa and the tetragonal-cubic transition at 11 GPa, at room temperature. © 2001 Elsevier Science Ltd. All rights reserved.

Kobayashi Y.;Endo S.;Deguchi K.;Ming L. C.;Zou G.

Solid State Communications

2001

X-Ray diffraction studies were carried out on the distorted perovskite La0.5-xBixCa0.5MnO3 (x=0, 0.05, 0.1, 0.15, 0.2, 0.25) under high pressure at room temperature by the energy-dispersive technique. The unusual expansion of the 202-040 d-spacing under pressure was observed and accompanied by a remarkable decrease of the Jahn-Teller distortion in MnO6 octahedra. The change of the Mn-O bond angle brings about the disappearance of the basal-plane distortion mode Q2. The substitution of Bi³⁺ for La³⁺ in the system introduces more distortions, which is ascribed to the unique lone pair characteristics of bismuth. © 2001 Elsevier Science B.V.

Wang Xin;Cui Qiliang;Pan Yuewu;Gao Wei;Zhang Jian;Zou Guangtian

Journal of Alloys and Compounds

2001

There is a widespread interest in searching for materials that are used to synthesize more efficient thermoelectric devices for cooling and power generation applications. We report on lead telluride (PbTe) compounds which have been synthesized by the high pressure and high temperature method. The thermoelectric properties in PbTe synthesized by high pressure and high temperature were strongly increased. A ZT value of 0.87 for PbTe measured at ambient temperature and pressure has been achieved in our experiment. This value is nearly 20 times larger than the reported values for PbTe synthesized at ambient pressure, and approximately equal to that of Bi 2 Te 3 . These results indicate that the technique of high pressure and high temperature is a useful tool to obtain materials of improved properties, and highly efficient thermoelectric materials may be expected. © 2002 Elsevier Science Ltd. B.V. All rights reserved.

Zhu P. W.;Jia X.;Chen H. Y.;Guo W. L.;Chen L. X.;Li D. M.;Ma H. A.;Ren G. Z.;Zou G. T.

Solid State Communications

2002

We study the energy-dispersive x-ray diffraction and Raman scattering of LiTaO3at high pressure. The result remains stable up to 36 GPa. The average isothermal bulk modulus and its pressure derivative are obtained to be ko= (225 ± 6) GPa and k′o= 1.3 ± 0.5 at zero pressure by the Birch-Murnaghan equation of state and the "universal" equation of state. The linear incompressibility of LiTaO3between the a- and c-directions differs by a factor of four, which shows that the compression is anisotropic.

Zhang Wei-Wei;Cui Qi-Liang;Pan Yue-Wu;Dong Shu-Shan;Zou Guang-Tian;Liu Jing

Chinese Physics Letters

2002

Superhard MgB 2 bulk material with a golden metallic shine was synthesized by high-pressure sintering for 8 h at 5.5 GPa and different temperatures. Appropriate pressure and temperature conditions for synthesizing polycrystalline MgB 2 with high hardness were investigated. The samples were characterized by means of atomic force microscopy and x-ray diffraction. The Vickers hardness, bulk density, and electrical resistivity were measured at room temperature.

Ma H. A.;Jia X. P.;Chen L. X.;Zhu P. W.;Ren G. Z.;Guo W. L.;Fu X. Q.;Zou G. T.;Ren Z. A.;Che G. C.;Zhao Z. X.

Journal of Physics Condensed Matter

2002

Pressure-induced behaviours of 2p energy levels of lithium in solid H2 are investigated by using the path integral Monte Carlo method with a constant-pressure ensemble (NPT). For the doped solid where a Li atom replaces one H2 molecule, the splittings between the three degenerate energy levels of the Li atomic 2p excited state are equal. For the doped solid where in Li atom replaces two H2 molecules, a novel different split of the three 2p energy levels is observed. An increase in pressure results in a significant shift of the individual 2p energy levels of the Li atom. The centroid of the 2p energy levels takes on a fascinating pressure dependence in which, with increasing pressure, the centroid of the 2p energy levels shifts towards higher energy below a turning pressure (Pt), arrives at the highest energy at Pt, then shifts towards lower energy above Pt.

Ma Y. M.;Cui T.;Zou G. T.

Journal of Physics Condensed Matter

2002

In situ high-pressure energy-dispersive x-ray diffraction measurements on α-LiIO3have been performed by using a diamond anvil cell device with synchrotron radiation up to 75 GPa at room temperature. No new phase was found. The second Birch-Murnaghan equation of state is fitted with B0= 55 ± 3 GPa for the zero-pressure bulk modulus, B0′ = 2.9 ± 0.4 for its pressure derivative.

Zhang W. W.;Cui Q. L.;Pan Y. W.;Dong S. S.;Zou G. T.;Liu J.

Journal of Physics Condensed Matter

2002

In order to prepare bulk C 3 N 4 , high-pressure pyrolysis of melamine (C 3 N 6 H 6 ) at different temperatures was carried out. The products were characterized by C, N, H element analysis, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and x-ray diffractometry. The results of the analysis reveal that graphitic phase C 3 N 4 has been synthesized. It provides a novel route to synthesis of the theoretical superhard cubic C 3 N 4 and other C 3 N 4 phases from organic compounds by a high-pressure and high-temperature method.

Ma H. A.;Jia X. P.;Chen L. X.;Zhu P. W.;Guo W. L.;Guo X. B.;Wang Y. D.;Li S. Q.;Zou G. T.;Zhang Grace;Bex Phillip

Journal of Physics Condensed Matter

2002

In this paper, we investigate the pressure-induced structural transition of α-Ga 2 O 3 powder by means of energy-dispersive x-ray diffraction (EDXD) measurements. The EDXD results show that, with increase of pressure, a new pressure-induced phase appears. The new tetragonal structure (β-Ga 2 O 3 ) can remain stable over the pressure range (≤38 GPa) under study.

Tu Baozhao;Cui Qiliang;Xu Peng;Wang Xin;Gao Wei;Wang Chengxin;Liu Jing;Zou Guangtian

Journal of Physics Condensed Matter

2002