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We studied the temperature and pressure structural stability of 5 nm BaTiO3 particles by using high resolution synchrotron X-ray diffraction, high pressure Raman spectroscopy, and high pressure impedance technique. A coexistence of the tetragonal and orthorhombic phases is observed in 5 nm Barium titanate BaTiO3 particles with weight fractions 67(6.6)% and 33(8.0)% at ambient condition, respectively. In the temperature range from -123 °C to 177 °C, the phase boundaries of 5 nm BaTiO3 are diffusive and several phases coexist. Pressure dependent Raman spectra of 5 nm BaTiO3 indicates that there exist two phase transitions: the first is at 7.5 GPa when the coexisting phases of orthorhombic and tetragonal undergoes transition to tetragonal phase; the second is around 17.3 GPa when the tetragonal transforms to cubic phase. Observed transitions were confirmed by the high pressure impedance property measurement. [ABSTRACT FROM AUTHOR]

Temperature dependent-electrical resistance of n-type Bi2Te3 was investigated under high pressure. Superconductivity was detected at 4.9 GPa with Tconset = 2.8 K. Resistance and Tc suggest that there are two electronic phase transitions below 10 GPa. We conjecture that the bulk insulating phase first changes to semimetal and then to metal. The evolution of the Hall coefficient is qualitatively consistent with the proposed electronic phase transition. The origin of superconductivity and topological properties are also discussed. [ABSTRACT FROM AUTHOR]

Temperature dependent-electrical resistance of n-type Bi2Te3 was investigated under high pressure. Superconductivity was detected at 4.9 GPa with Tconset = 2.8 K. Resistance and Tc suggest that there are two electronic phase transitions below 10 GPa. We conjecture that the bulk insulating phase first changes to semimetal and then to metal. The evolution of the Hall coefficient is qualitatively consistent with the proposed electronic phase transition. The origin of superconductivity and topological properties are also discussed. [ABSTRACT FROM AUTHOR]