Shoichi Endo

The Generation of Ultrahigh Hydrostatic Pressures by a Split Sphere Apparatus

A split sphere apparatus has been developed to generate exceedingly high hydrostatic pressures more than 300 kilobars at temperatures over 1500°C in a sample chamber of ample volume. The calibration of pressures is made by the use of known phase transition points in Bi, Fe, and Pb. The calibration above the Pb point (161 kilobars) is discussed in terms of resistance changes for In and CdS previously reported by Drickamer et al.

Electrical Properties of Black Phosphorus Single Crystals

Large single crystals of black phosphorus have been grown under high pressure, and by using the crystals, the Hall measurements have been done in a range from 4.2 K to 550 K. All the undoped samples have exhibited p -type conduction, while we have succeeded in obtaining n -type crystals by doping Te impurity. The effective acceptor concentrations N A -N D of the p -type samples and those of donor in n -type samples N D -N A have been in the range of 2∼5×10 15 cm -3 and 2∼3×10 16 cm -3 , respectively. From the intrinsic range of the conductivity, the energy gap has been estimated to be 0.335 eV, The acceptor and donor activation energies have been determined to be ∼18 meV and ∼39 meV, respectively. The Hall mobility of the hole reaches its maximum of 6.5×10 4 cm 2 /V·sec around 20 K. The anisotropies of the conductivity and the mobility along the three crystal axes have been investigated.

Baddeleyite-Type High-Pressure Phase of TiO2

A high-pressure phase of TiO2, which had been observed by shock-wave experiments and remained unresolved, has been studied by in situ x-ray diffraction. The single phase was formed at 20 gigapascals and 770�C with the use of sintered-diamond multianvils; it has the same structure as baddeleyite, the stable phase of ZrO2 at ambient conditions. The coordination number of Ti increases from six to seven across the rutile to baddeleyite transition, and the volume is reduced by approximately 9 percent.

Growth of Large Single Crystals of Black Phosphorus under High Pressure

A large volume high pressure apparatus has made it possible to grow large single crystals of black phosphorus, P. After converting red P powder into black P under a high pressure of 10 kbar at high temperature, a melt of polycrystalline black P has been gradually solidified to bring about the growth of single crystals. Crystal sizes larger than 5×5×10 mm3 are, for the first time, adequate for various measurements of the physical properties expected for this narrow gap semiconductor with a special layered structure. An X-ray analysis has proved the good single crystalline structure.

Compression behavior of CdS and BP up to 68 GPa

High‐pressure in situ x‐ray diffraction study on CdS and BP was performed using a diamond anvil cell up to 68 GPa at room temperature. The rocksalt structure type CdS was found to transform to a new high‐pressure polymorph at about 56 GPa. X‐ray diffraction pattern of the new high‐pressure polymorph was successfully indexed by the lowest temperature KCN structure type with the distorted rocksalt structure. Volume change accompanied with the transformation was calculated to be about 0.8%. This small volume change may be responsible to the undetectable change in refractive index of CdS at the transformation. No phase transformation was observed on BP: the zincblende structure is stable up to 68 GPa.

Olivine-Spinel transformation in a natural forsterite

Abstract The olivine-spinel transformation in a natural forsterite is studied in the pressure range 98–130 kb and the temperature range 700–1100 °C. The reaction boundary at which olivine solid solution of 93% Mg 2 SiO 4 and 7% Fe 2 SiO 4 breaks down to spinel solid solution and olivine solid solution is determined as P (kb) = 0.054 T (°C)+61. The entropy change of the metastable olivine-spinel transformation in pure Mg 2 SiO 4 is calculated to be − 4.4 cal/° · mole at 100 kb and 1000 °C.

Far-infrared cyclotron resonance absorptions in black phosphorus single crystals

Far-infrared cyclotron resonance absorptions in black phosphorus have been measured by using relatively large single crystals of n -type and p -type prepared by a large volume-high pressure technique at high temperature. The effective masses of the electron and the hole in the crystals have been determined along the three principal crystal axes and found to have appreciably large anisotropies. The experimental masses have been compared with the theoretical results so far published. The temperature and magnetic field dependences of the relaxation times of the carriers obtained from the half-widths of the cyclotron resonant peaks are discussed in the comparisons with the carrier mobilities in the results of the Hall measurements previously reported.

Electrical and optical properties of black phosphorus single crystals

Abstract Large single crystals of black phosphorus have been prepared by a large volume-high pressure technique at high temperature. Using the crystals, we have measured temperature dependences of the electrical conductivity and the Hall coefficient, the FIR cyclotron resonance absorption and the reflectance for synchrotron radiation. All samples obtained are p-type and the Hall mobility reaches 5×10 4 cm 2 v·sec around 20K. The anisotropies of the effective mass, the Hall mobility and the SOR reflectance along the three crystal directions, a, b, and c, have been observed.

Superconductivity of Calcium under High Pressures

Electrical resistance of Ca is measured under pressures up to 150 GPa and at temperatures down to 0.05 K. Superconductivity is observed at temperatures below 3 K under pressures above 85 GPa. The superconducting transition temperature increases linearly with increasing pressure and reaches about 15 K at 150 GPa.

57Fe Mössbauer study under high pressure; ε-Fe and Fe2O3

Using diamond anvil cell, the57Fe Mössbauer spectra of pure iron foil and α-Fe2O3 powder under high pressure have been measured at room temperature.57Fe Mössbauer spectra of α-Fe were measured from 15 GPa to 45 GPa. Isomer shift value decreased and the quadrupole splitting slightly increased as the pressure increased.57Fe Mössbauer spectra of Fe2O3 under high pressure up to 72 GPa were observed. Above 52 GPa, the new lines appeared at the center portion of the spectrum corresponding to the new high pressure phase. The spectrum of new high pressure phase consisted of 6-line splitting and doublet, suggesting the existence of the two different kinds of iron states in it.