Wright Ng

Structural studies of III–V and group IV semiconductors at high pressure

Abstract Extensive new structural results on II–VI, III–V and group IV semiconductors under pressure have been obtained over the past two years at SRS Daresbury, using angle-dispersive techniques and an image-plate detector. In this paper, a brief overview is presented of recent work on Si, Ge, GaSb, InSb, InAs, InP and GaAs.

Structural studies of II-VI semiconductors at high pressure

Abstract Extensive new structural results on II–VI, III–V and group IV semiconductors under pressure have been obtained over the past two years at SRS Daresbury, using angle-dispersive techniques and an image-plate detector. In this paper, a brief overview is presented of recent work on ZnTe, CdTe, HgTe, HgS.

High-pressure neutron-diffraction studies of KH2PO4-type phase transitions as Tc tends to ok

Abstract A neutron-diffraction study has been carried out on KH2PO4 at 16.5kbars and 10K, close to the point at which the transition temperature, Tc, falls to OK at 17.1kbars. The results suggest that under these conditions, the H atoms are still disordered over two sites with a separation, δ, of 0.22(2)A. Comparison with results from previous structural studies of other other H-bonded systems suggests that Tc is linearly related to δ in each case and that each system has the same critical value of δ as Tc ↪

Crystal‐structure studies of III‐V and group IV semiconductors using angle‐dispersive diffraction techniques with an image‐plate detector

Angle‐dispersive powder‐diffraction techniques, coupled with an image‐plate area detector and synchrotron radiation, have been used to study the crystal structures of III‐V and group IV semiconductors at high pressure. A new phase of silicon has been found between the well‐known β‐tin and simple‐hexagonal phases, while germanium samples downloaded rapidly from 14 GPa to ambient pressure have been found to transform to the so‐called BC8 structure rather than to ST12. Studies of InP have confirmed the transition to an ordered NaCl structure at ∼10 GPa.

Microstructural aspects of reconstructive phase transitions under pressure

A discussion of the main microstructural effects seen in high pressure powder diffraction is presented. Data collected on InP, CdTe, and HgTe are used to illustrate the two main effects, preferred orientation and peak width variation. These must be accurately modeled if Rietveld refinement of the structure is to be performed. It is possible that information about transition mechanisms can be extracted from the microstructure.

Neutron-diffraction studies of the heavy-atom structure in h-ordering materials

Abstract We have made a high-resolution neutron-diffraction study of KD2PO4 (DKDP) at Tc+5K. The results indicate that above Tc, in the paraelectric phase, the thermal motion of the P atom is highly anharmonic along the z axis, and can be better modelled using a disordered three-site distribution. Analysis of the P-atom thermal motion in a neutron-diffraction study of KH2PO4 (KDP) at 16.5kbars and 10K, close to the point where Tc ↪ ok, indicates that the separation of the disordered P-atom sites remains relatively unchanged on cooling or under pressure. This may suggest that Tc is not directly related to the P-atom separation.