Energy-dispersive x-ray diffraction studies are 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. The unusual expansion of the 202-040 d-spacing under pressure is observed, and the change of the Mn-O bond angle brings about the disappearance of the basal-plane Q2 distortion mode. With doping content increasing, a shoulder peak appears in the observed main peak of La0.25Bi0.25Ca0.5MnO3 at 43.9 GPa. The pressure-enhanced interactions between charge, orbital, and coupling with the lattice distortion are discussed.

Wang Xin;Cui Qiliang;Pan Yuewu;Zou Guangtian

Journal of Physics Condensed Matter

2002

Diamond films have been grown on polished Si substrates seeded with nanocrystalline diamond powder colloid using hot-filament chemical vapour deposition. Instead of using the conventional gaseous carbon source, a carbonized W filament was used as the carbon source. The only feeding gas was hydrogen. Compared with those produced by traditional methods, the polycrystalline diamond grown by this new method has smaller grain size. The growth mechanism is also discussed.

Liu Hongwu;Wang Chengxin;Gao Chunxiao;Han Yonghao;Luo Jifeng;Zou Guangtian;Wen Chao

Journal of Physics Condensed Matter

2002

We have studied the high-pressure and high-temperature behaviour of α-PbO 2 -type TiO 2 -SnO 2 (5 mol%) nanocomposite up to 62.3 GPa and 1700 K in a laser-heated diamond-anvil cell by means of synchrotron energy-dispersive x-ray diffraction. We found that it transforms to the baddeleyite phase at 19.4 GPa at room temperature. This phase was stable up to about 40 GPa. At 62.3 GPa and 1700 K, the diffraction pattern showed that there exists another nonquenchable phase. We discussed the mechanisms for these high-pressure transformations in α-PbO 2 -type TiO 2 -SnO 2 (5 mol%) nanocomposite.

Luo W.;Zou G. T.;Ma Y. Z.;Mao H. K.;Wang Z. C.;Wang Y.

Journal of Physics Condensed Matter

2002

In situ high-pressure energy-dispersive X-ray diffraction (EDXRD) experiments on melamine (C 3 N 6 H 6 ) have been carried out using diamond anvil cell (DAC) with synchrotron radiation source. In the pressure range from ambient pressure up to 14.7 GPa, two pressure-induced structure phase transitions, from monoclinic to triclinic structure at about 1.3 GPa and from triclinic to orthorhombic structure at about 8.2 GPa, are observed. The crystal structures of melamine at different pressures are built by using Materials Studio (MS) based on the principle of energy minimization. © 2002 Elsevier Science B.V. All rights reserved.

Ma H. A.;Jia X.;Cui Q. L.;Pan Y. W.;Zhu P. W.;Liu B. B.;Liu H. J.;Wang X. C.;Zou G. T.;Liu J.

Chemical Physics Letters

2003

The results of measurements of X-ray photoelectron and infrared absorption spectra in the manganese oxides La0.5-xBixCa0.5MnO3 (x=0, 0.05, 0.1, 0.15, 0.2, 0.25) are presented. Compared with the energy exchange splitting in different valency Mn compounds, the average Mn valency in our samples is close to 3.5+. Infrared spectra show two strong absorption bands located around 600 and 420 cm^-1, which can be ascribed to the internal phonon modes νs and νb. As the doping x increases, the band frequency of νs decreases while the νb band remains invariant, and a reversal of the intensity ratio of νs to νb is also observed. These results reflect the changes of the Mn-O bond length and the Mn-O-Mn bond angle of MnO6 octahedra along with the doping, and the changes are mainly influenced by the unique 6s² lone pair character of the doped Bi ions. © 2002 Elsevier Science B.V. All rights reserved.

Wang Xin;Cui Qiliang;Pan Yuewu;Zou Guangtian

Journal of Alloys and Compounds

2003

High temperature Raman spectra of Sr2Bi4Ti5O18 have been investigated. A first order phase transition induced by a soft mode occurs at its Curie temperature. The soft mode is connected with the unstable Bi³⁺ion displacement in the perovskite-like layers. © 1994.

Zou Guangtian;Liu Jianjun;Cui Qiliang;Yang Haibin

Physics Letters A

1994

The Raman spectra of the system Ba2Bi4-xLaxTi5O18, at room temperature for 0 < × < 2 in the range 25-1000 cm^-1, were investigated. A first order phase transition occurs at about x = 1.2. The phase transition is attributed to the instability of the perovskite-like layers.

Liu Jianjun;Jin Yanrong;Gao Chunxiao;Zou Guangtian

Physics Letters Section A General Atomic and Solid State Physics

1996

Raman spectra of layered ferroelectrics Sr2+cursive chiBi4-cursive chiTi5-cursive chiNbcursive chiO18(0 ≤ cursive chi ≤ 2) and Sr2Bi4-cursive chiLacursive chiTi5O18at room temperature in the range of 20-1000 cm^-1were investigated. Vibration modes were assigned with the internal mode approach. Two doping-induced structure phase transitions were observed at about cursive chi = 0.5 and 1.25 for Sr2+cursive chiBi4-cursive chiTi5-cursive chiNbcursive chiO18, separately.

Han Jie;Zou Guang-Tian;Ge Zhong-Jiu

Chinese Physics Letters

1999

The temperature dependence (5-45 K) of the absorption spectra of a Li atom doped in solid hydrogen at P = 1.2 GPa is investigated using the path integral Monte Carlo (PIMC) method with a constant pressure ensemble. Higher temperature in our research range does not cause rearrangement of the trapping site structures. The significantly broadening and spreading of the three component absorptions with increasing temperature are observed. For the trapping site structures belonging to lower symmetry point groups, the singlet to doublet splitting decreases as temperature gets larger. An insight on the temperature-induced behaviors of the Li absorption spectrum in the doped system has been made by using the simulated results.

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

Journal of Low Temperature Physics

2001

Raman spectra of Na0.5Bi4.5Ti4O15 have been investigated under hydrostatic pressure up to 10 GPa. Two pressure-induced phase transitions have been observed at about 1.94 GPa and 9.0 GPa, respectively.

Liu Jianjun;Jin Yanrong;Gao Chunxiao;Zou Guangtian

Physics Letters Section A General Atomic and Solid State Physics

1996