Neutron diffraction evidence for the spin-reorientational transition in FeBO3 at high pressures

The spin-reorientational transition from the state with “easy-plane” anisotropy to the state with “easy-axis” anisotropy—a pressure analogue of the Morin temperature transition in hematite— was detected in iron borate at a pressure of P～17 kbar at room temperature by the neutron diffraction method.     

Neutron diffraction evidence for magnetic phase transition in Europium selenide

The results of a single crystal neutron diffraction study of europium selenide EuSe in zero external magnetic field are reported. At 4.2°K europium selenide is antiferromagnetically ordered according to an oscillating type of spin configuration. Partial ferromagnetism is observed at 1.9°K, in agreement with previous measurements [1, 2]. Concerning this low temperature phase a model with two coexistent magnetic phases is proposed.     

Neutron diffraction investigation of the magnetic structure of the Mn2Sb pnictide at high pressures

This paper reports on the results of investigations into the influence of high pressures (up to 5.3 GPa) at T=300 K on the magnetic structure of the Mn₂Sb pnictide. The crystal and magnetic structures of the Mn₂Sb compound are studied using a direct neutron diffraction method. It is demonstrated that the magnetic ferrimagnet-antiferromagnet phase transition, which is observed in a number of Mn₂Sb-based substitutional solid solutions upon chemical compression of the Mn₂Sb crystal lattice, does not occur in the Mn₂Sb compound under high pressures in the aforementioned range due to an anisotropic pressure-stimulated strain in the Mn₂Sb lattice. At pressures P≥2.8 GPa, the Mn₂Sb compound is characterized by a spin reorientation with respect to the tetragonal axis and the basal plane of the crystal lattice.     

High resolution X-ray diffraction studies at high pressures

Abstract

The principal sources of systematic error in high-pressure x-ray structure determination with a diamond anvil cell have been studied in detail. The results of these studies have been used to develop techniques to minimise or correct for these effects.     

Neutron diffraction studies of hydrogen-bonded ices at high pressure

Abstract

The development of the Paris-Edinburgh cell has extended the pressure range for neutron diffraction by a full order of magnitude to 30 GPa. This advance has provided a wealth of new information on the high-pressure behaviour of ices such as water-ice, ammonia, methane and hydrogen sulphide. We have now put in place technique developments to permit loading of water-gas mixtures into the Paris-Edinburgh cell.     

Neutron diffraction investigation of the structural transition in HgSe1−x Sx ternary mercury chalcogenide systems at high pressures

The structure of HgSe_1?x S_x ternary mercury chalcogenides at high pressures up to 35 kbar is investigated by neutron diffraction. It is found under pressure, that the HgSe_1?x S_x compounds undergo, a phase transition from the cubic sphalerite-type to the hexagonal cinnabar-type structure, which is accompanied by a jump-wise change in the unit cell volume and interatomic distances. The unit cell parameters and the positional parameters of Hg and Se (S) atoms in the high-pressure hexagonal phase are determined. A two-phase state is revealed in the phase transition region.     

Neutron scattering study of the phase transition in s-triazine at high pressure

The elastic transition in s-triazine (C₃N₃H₃) from a trigonal ($\text{R}\text{3}\text{c}$) high temperature (low pressure) structure to a monoclinic (C2/c) low temperature (high pressure) phase has been investigated at pressures up to 5 kbar using neutron scattering techniques. Neutron diffraction was used to measure the pressure dependence of the order parameter and inelastic scattering to study the softening of the transverse acoustic phonon modes on three isotherms. In both cases the effect of pressure on the transition is found to be described primarily by that on the temperature of the transition.     

White-beam X-ray diffraction and radiography studies on high-boron-containing borosilicate glass at high pressures

ABSTRACT

Multi-angle energy-dispersive X-ray diffraction studies and white-beam X-ray radiography were conducted with a cylindrically shaped (1?mm diameter and 0.7?mm high) high-boron-content borosilicate glass sample (17.6% B₂O₃) to a pressure of 13.7?GPa using a Paris-Edinburgh (PE) press at Beamline 16-BM-B, HPCAT of the Advanced Photon Source. The measured structure factor S(q) to large q?=?19 Å^?1 is used to determine information about the internuclear bond distances between various species of atoms within the glass sample. Sample pressure was determined with gold as a pressure standard. The sample height as measured by radiography showed an overall uniaxial compression of 22.5% at 13.7?GPa with 10.6% permanent compaction after decompression to ambient conditions. The reduced pair distribution function G(r) was extracted and Si–O, O–O and Si–Si bond distances were measured as a function of pressure. Raman spectroscopy of the pressure recovered sample as compared to starting material showed blue-shift and changes in intensity and widths of Raman bands associated with silicate and four-coordinated boron.     

Neutron diffraction study of the structural phase transition in SnS and SnSe

The structural phase transitions in SnS and SnSe have been investigated by neutron diffraction in the temperature range 295–1000 K using a high temperature furnace. Accurate positional and thermal parameters have been obtained as a function of temperature both in the α- (GeS-type, B16) and β-phase (TlI-type, B33). These investigations indicate that the α → β phase transitions in SnS and SnSe are of second order displacive type, and consist mainly of the continuous movement of Sn and S/Se atoms almost entirely along the [100] direction, and suggest the soft-mode behaviour of a zone-boundary phonon of the β-phase.     

Effect of carbon materials on the graphite-diamond phase transition at high pressures and temperatures

Experimental data are used in an attempt to unravel the mechanism underlying the effect of modification of a graphite blend by fullerenes on the diamond synthesis at high pressures and temperatures in the presence of metal catalysts. Diamonds have been synthesized under different conditions in a wide range of temperatures and at different pressures, and the effects of blend modification by fullerenes and by addition of natural microcrystalline diamonds to a blend on the diamond synthesis at high pressures and temperatures have been compared.     

Electron transport properties of lithium and phase transitions at high pressures

The electric resistivity and thermopower of lithium have been precisely measured at high pressures (up to 8 GPa) and temperatures from room temperature to 100°C. Transition to the fcc phase of lithium has been analyzed. The hysteresis of the direct and inverse transitions is 0.3 GPa at room temperature, decreases slightly with an increase in the temperature, and is almost independent of the prehistory of the sample. The phase transition line on the P-T diagram has a positive slope of dP/dT = 0.03 GPa/K. It is assumed that the fcc phase of lithium, which is stable at a high pressure, can appear for kinetic regions from the 9R phase, which is intermediate in energy between the bcc and fcc modifications.     

Neutron diffraction study of UAs in high magnetic fields

Magnetization experiments have shown that at low temperature and in an applied magnetic field of ～90 kOe antiferromagnetic (AF) uranium arsenide transforms to a new ferrimagnetic state. The high-field transition produces a state with magnetic components $\text{parallel}$ to the applied field. A small ferromagnetic component (0.4 μ_B) is seen in magnetization experiments but with neutron diffraction we have observed directly the large AF component (～ 1.8 μ_B) which has a $\text{q}$ value of 0.58 ± 0.01 $\text{c}$¹ in contrast to the zero field type IA structure with $\text{q}\text{= (0,0,0.50)}$. This transition is quite different from that occuring in the conventional spin-flop transition.     

Neutron powder diffraction studies at high pressure using a pulsed neutron source

Abstract

High-pressure neutron-diffraction experiments using the time-of-flight (TOF) method are presented. We first introduce the helium-gas pressure system at Argonne's Intense Pulsed Neutron Source (IPNS) with the Special Environment Powder Diffractometer (SEPD). The results for TIBa₂CuO₆₊₈, and La_2?x, Sr_x, CuO_4–8 are briefly reviewed. We then introduce the present situation in Japan. We have been developing a high-pressure system on high-resolution powder diffractometer (HRP) which was much improved recently and renamed VEGA at KEK. The best resolution of 0.45% was obtained at VEGA. The preliminary results for YBa₂, Cu₄O₈, and HgBa₂, CuO₄₊₈, are presented and compared with the SEPD data.     

Neutron diffraction study of the smectic C-smectic a phase transition of TBBA

The smectic C-smectic A transition of terephtal bis butyl aniline (TBBA) is investigated using neutron diffraction. The critical exponent relating the tilt angle to the reduced temperature is found to be β = 0.44 ± 0.04. Comparison with results obtained by other methods and with theoretical predictions is presented.     

In-situ combined X-ray diffraction and electrical resistance measurements at high pressures and temperatures in diamond anvil cells

A method of simultaneous X-ray diffraction and electrical resistance measurements of materials in a diamond anvil cell has been developed. The experimental arrangement for the electrical measurements uses a gasket as a part of the electrode scheme. Application of the new methodology is demonstrated on the examples of the study of high-pressure high-temperature behavior of Pr and Fe–Ni alloys. Simultaneously obtained diffraction and resistance data provide the different, from earlier studies, interpretations of the topology of the dhcp–fcc phase transition in the phase diagram of Pr. Namely, the shape of a hysteretic region is mostly defined by kinetics of the dhcp phase growth rather than by thermodynamic driving force at the fcc to dhcp phase transformation. The results of combined X-ray diffraction and resistance measurements of Fe0.₈Ni0.₂ alloy up to 18 GPa and 425 K are reported along with the complementary resistance measurements of Fe0.₉Ni0.₁ alloy.     

The application of neutron powder diffraction techniques for crystallographic studies at high pressures

Abstract

For phase transition studies, neutron powder diffraction offers a number of important advantages over x-ray based techniques, for example ab-initio structural determination. There are two distinct methods using either monochromatic angular dispersive geometry on a reactor cold source or time-of-flight energy-dispersive techniques requiring a pulsed neutron source. Both techniques offer comparable resolution but have differing advantages for high pressure studies. Recent studies illustrate the benefits of the two methods and the application of these to solve unknown crystal structures.     

Electron and magnetic transport in the diluted magnetic semiconductor CdGeAs2<Mn>at high pressures

In CdGeAs₂<Mn>, a metamagnetic phase transition and a negative magnetic resistance induced by high pressure were found and studied.