Jin Chang-Qing

Hydrostaticity of Pressure Media in Diamond Anvil Cells

Hydrostaticity under high pressure of several materials from solid, fluid to gas, which are widely used as pressure media in modern high-pressure experiments, is investigated in diamond anvil cells. Judging from the R-line widths and R1 – R2 peak separation of Ruby fluorescence, the inert argon gas is hydrostatic up to about 30 GPa. The behavior of silicon oil is found to be similar to argon at pressures less than 10 GPa, while the widening of R-lines and increase of R1 – R2 peak separation at higher pressure loads indicate a significant degradation of hydrostaticity. Therefore silicon oil is considered as a good pressure medium at pressures less than 10 GPa but poor at higher pressures.

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.

High-pressure synthesis of MgB2 superconductor with T-c above 39 K

We report on the high-pressure synthesis and superconductivity of MgB2 intermetallic compounds. The compounds have been obtained through high-pressure sintering of the mixtures of magnesium and boron fine powders under 5.0 GPa and at ~1000°C for 30 min. Magnetic measurements using a SQUID magnetometer show the sharp bulk superconducting transition above 39 K; the four-probe dc resistivity measurements indicate the highly-conductive normal state and sharp superconducting transition. The results highlight that high-pressure synthesis would be a promising way to promote the studies of this new kind of intermetallic superconductors.We report on the high-pressure synthesis and superconductivity of MgB2 intermetallic compounds. The compounds have been obtained through high-pressure sintering of the mixtures of magnesium and boron fine powders under 5.0 GPa and at similar to 1000 degreesC for 30 min. Magnetic measurements using a SQUID magnetometer show the sharp bulk superconducting transition above 39 K; the four-probe de resistivity measurements indicate the highly-conductive normal state and sharp superconducting transition. The results highlight that high-pressure synthesis would be a promising way to promote the studies of this new kind of intermetallic superconductors.

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.

Measurement of R Line Fluorescence in Ruby Using the Diamond Anvil Cell at Low Temperature

Using our custom-built high-pressure cryostat we have performed the measurements of the R line fluorescence of ruby in the diamond anvil cell from room temperature down to 90 K. The maximum pressure was 11.1 GPa. By computer curve fitting, different equations have been found for functions of wavenumber versus temperature between ambient pressure and 2.7 GPa. The changes of the shape and linewidth of R lines were observed.

Effects of pressure and/or magnetism on superconductivity of δ-MoN single crystal *

Effects of pressure and/or magnetism on the critical superconducting temperature (Tc) of δ-MoN single crystal were investigated using a Maglab system. The δ-MoN single crystal was synthesized at extreme conditions of high pressure and high temperature. The carrier density of δ-MoN single crystal as a function of applied pressure was determined using Hall coefficient measurement.

A Simple System to Measure Superconducting Transition Temperature at High Pressure

A simple hydride system is fabricated to measure the superconducting transition temperature Tc under high pressure using a diamond anvil cell (DAC). The system is designed with centrosymetric coils around the diamond that makes it easy to keep balance between the pick-up coil and the inductance coil, while the superconducting states can be modulated with a low-frequency small external magnetic field. Using the device we successfully obtain the Tc evolution as a function of applied pressure up to 10 GPa for YBa2Cu3O6+δ superconductor single crystal.