Yu Ri-Cheng

Structural Stability of CaCuMn6O12 under High Pressure and Low Temperature

In situ high pressure energy-dispersive x-ray synchrotron radiation diffraction and resistance experiments are carried out on CaCuMn6O12. Its crystal structure is stable in the measured pressure range. The equation of state of CaCuMn6O12 is obtained from the V/V0−P relationship (V and V0 are the volumes at pressure P and at atmosphere). The bulk modulus B0 is calculated based on the Birch–Murnaghan equation. Low temperature x-ray diffraction shows no phase transition occurring down to 160 K.

Isostructural Phase Transition of TiN under High Pressure

In situ high-pressure energy dispersive x-ray diffraction experiments on polycrystalline powder TiN with NaCl-type structure have been conducted with the pressure up to 30.1 GPa by using the diamond anvil cell instrument with synchrotron radiation at room tempearture. The experimental results suggested that an isostructural phase transition might exist at about 7 GPa as revealed by the discontinuity of V/V0 with pressure.In situ high-pressure energy dispersive x-ray diffraction experiments on polycrystalline powder TiN with NaCl-type structure have been conducted with the pressure up to 30.1 GPa by using a diamond anvil cell instrument with synchrotron radiation at room temperature. The experimental results suggest that an isostructural phase transition might exist at about 7 GPa as revealed by the discontinuity of V/V0 with pressure.

Metallization of Cu3N Semiconductor under High Pressure

Using the four-probe method, we investigate the electrical conductivity of Cu3N under high pressure with the diamond anvil cell. Cu3N is a semiconductor at ambient pressure showing a band gap about 1 eV. With the application of quasi-hydrostatic pressures, its resistance decreases dramatically over five orders of magnitude from ambient to 9 GPa. The compound became a metal at pressure about 5.5 GPa, which is in well agreement with the recent first principle calculation.

Pressure Effects on the Magnetic Phase Transition of Mn3SnC1−xNx (x = 0, 0.5)

The electronic transport properties of Mn3SnC and Mn3SnC0.5N0.5 were measured under pressures up to 1.8 GPa. At ambient pressure, an abrupt increase of resistance occurs around the temperature of magnetic phase transition in both samples. The transition temperature Tc from paramagnetic to ferrimagnetic state decreases linearly at rates of 12.6 and 6.3K/GPa with pressure for Mn3SnC and Mn3SnC0.5N0.5, respectively. This phenomenon could be understood by the Labbe-Jardin tight binding approximation model.

Compressibility of lattice parameters of several layered compounds

The lattice parameters of AlB2, MgB2 and TiB2 under pressures are determined with a high-energy synchrotron source in a diamond anvil cell. The experimental results indicate that these three compounds have different mechanical behaviour under pressures, TiB2 is the hardest and MgB2 is the softest among the three materials. The phenomena are explained in terms of bonding strength in the crystal. Our results may be helpful for understating the decrease of the superconducting transition temperature of MgB2 under pressures.

Pressure-induced phase transition in BaTiO(3) nanocrystals

The crystal structure and electric properties of BaTiO(3) nanocrystals are studied by in situ high-pressure synchrotron radiation x-ray powder diffraction. The phase transition takes place not only in the samples of BaTiO(3) 14 nanocrystals that are tetragonal phase with grain sizes more than 100 nm, but also in the samples of BaTiO(3) nanocrystals that are cubic phase with grain sizes less than 100 nm. The pressures of phase transition are found to increase with decrease of the grain size from about 4 to 10 GPa, for crystallites ranging from 200 to 10,nm in radius. The bulk moduli are calculated according to Birch-Murnaghan state equation before and after the phase transition.

Synthesis and Structural Study of Sr2CuO3 + δ Superconductor under High Pressure

A single-phase Sr2CuO3 + δ superconductor is synthesized under high temperature and high pressure, in which oxygen atoms only partially occupy the apical sites next to the CuO2 planes and act as hole-dopants. The superconducting transition temperature with Tcmax = 75 K is achieved in the material. Structure analysis from x-ray powder diffraction data show that this material crystallizes into a K2NiF4 structure with tetragonal unit cell of a = 3. 795(3) A and c = 12. 507(1) A. Energy-dispersive synchrotron x-ray-diffraction studies at ambient are performed on powder samples of Sr2CuO3 + δ in a diamond-anvil cell at pressure up to 35 GPa. Anisotropic compressibility is found. Pressure-induced isostructural phase transition might exist as revealed by the discontinuous change of crystal cell volume V with pressure.

Enhanced MgB2 Superconductivity Under High Pressure

We report on in situ high-pressure studies up to 1.0?GPa on the MgB2 superconductor which was high-pressure synthesized. The as-prepared sample is of high quality in terms of sharp superconducting transition (Tc) at 39?K from the magnetic measurements. The in situ high-pressure measurements were carried out using a Be-Cu piston-cylinder-type instrument with mixed oil as the pressure transmitting medium which warrants a quasi-hydrostatic pressure environment at low temperature. The superconducting transitions were measured using the electrical conductance method. It is found that Tc increases by more than 1?K with pressure in the low-pressure range, before the Tc value decreases with the further increase of the pressure.

Absorption Range and Energy Shift of Surface Plasmon in Au Monomer and Dimer

The resonance behaviors of local surface plasmon resonance in Au monomer and dimer are characterized systemically by electron energy loss spectroscopy in a scanning transmission electron microscope. The measured absorption range is about 20 nm larger than the physical size of the Au nanoparticles and the resonance peak energy shows a red shift when the electron beam passes of the nanoparticles. The Au dimer displays similar behaviors. Numerical simulation also reproduces those experimental results.

Structural phase transitions of tellurium nanoplates under pressure

In situ high-pressure angle dispersive x-ray diffraction experiments using synchrotron radiation on Te nanoplates were carried out with a diamond anvil cell at room temperature. The results show that Te-I with a trigonal structure transforms to triclinic Te-II at about 4.9 GPa, Te-II transforms to monoclinic Te-III at about 8.0 GPa, Te-III turns to rhombohedral Te-IV at about 23.8 GPa, and Te-IV changes to body centered cubic Te-V at 27.6 GPa. The bulk moduli B0 of Te nanoplates are higher than those of Te bulk materials.