Sample environment equipment, cryostats, furnaces, pressure cells etc. are an essential adjunct to most neutron scattering experiments to induce the sample being studied into a phase or state of particular interest. He we give a brief overview of the diverse range of Sample Environment equipment that is currently in use, a background to its development and also some recent trends.

A review of sample environments in neutron scattering

The study of structural phase transitions that occur as the result of the application of pressure is still in its long-drawn-out infancy This is a direct result of the non-quenchability of structural phase transitions; their characterisation requires measurements of the material to be made in situ at high pressures Although structural phase transitions could be detected by simple macroscopic compression measurements in piston-cylinder apparatus when the volume change arising from the transition was sufficiently large (eg calcite by Bridgman 1939, and spodumene by Vaidya et al 1973) the limitations on sample access precluded their proper microscopic characterisation The development in the 1970s of in situ diffraction methods, specifically the diamond-anvil cell (DAC) for X-ray diffraction and various clamp and gas-pressure cells for neutron diffraction, allowed both the structure of high-pressure phases and the evolution of the unit-cell parameters of both the high- and low-symmetry phases involved in a phase transition to be determined Several classic studies of phase transitions at relatively low pressures were performed by high-pressure neutron diffraction methods in the 1970s and 1980s (eg Yelon et al 1974, Decker et al 1979), but the instrument time required for high-pressure studies (a result of limited sample access through, and attenuation by, the high-pressure cells as well as small sample sizes) limited the number of studies performed In addition, until the advent of the Paris-Edinburgh pressure cell which can achieve pressures of up to 25 GPa (Besson et al 1992, Klotz et al 1998), pressure cells for neutron diffraction were limited to maximum pressures of the order of 2 to 4 GPa In the past two decades the precision and accuracy of high-pressure X-ray diffraction methods has advanced considerably (see Hazen 2000) Single-crystal X-ray diffraction, which can be performed in the laboratory, is routine to pressures of …

High-Pressure Structural Phase Transitions

The application of neutron powder diffraction to the study of mineral behaviour at high temperature and high pressure is reviewed The characteristics of neutrons that make them particularly amenable to such studies are outlined, and recent techno- logical developments in the attainment of extreme sample environments are discussed These developments include the design of new high-pressure cells, hydrothermal cells, and furnaces that allow in situ diffraction under extreme conditions The application of this technology to problems of order-disorder in minerals is illustrated in a series of recent examples

Neutron powder diffraction of minerals at high pressures and temperatures some recent technical developments and scientific applications

High-pressure study on dioxolane silica sodalite (C3H6O2)2[Si12O24]—neutron and X-ray powder diffraction experiments

Solid-gas reactions play an important role in many technologically important processes from ore smelting to hydrogen storage and the synthesis of functional materials. In situ investigations are very useful for unraveling basic steps of such reactions, rationalizing them and gaining control. For investigating time-resolved solid-gas reactions, we have constructed a gas pressure cell for elastic neutron diffraction. By proper orientation of a single-crystal sapphire tube as sample holder, Bragg peaks from the container material can be completely avoided, thus yielding high-quality powder diffraction data with very clean diffraction background. This enables the extraction of high precision crystal structure data as a function of gas pressure and temperature (laser heating) in time-resolved studies. The potential of the gas pressure cell is demonstrated by in situ studies of the reaction of solids with hydrogen, which yielded detailed models of the reaction pathways including high quality crystal structures of reaction intermediates and products. These were used to predict successfully the existence of further metal hydrides, to explain unusual bonding properties, and to optimize the synthesis of metastable compounds.

A sapphire single-crystal cell for in situ neutron powder diffraction of solid-gas reactions

The construction principles of a new heatable large volume high-pressure cell for neutron powder diffraction, the Kiel–Berlin Cell II, are presented. The basic design is of the piston/cylinder type. The cell is designed to operate up to pressures of 3.5 GPa and temperatures above 800 K. First tests showed the mechanical stability of the cell to be ensured up to the corresponding necessary sample load of 50 tons and a prestress of 110 tons. The cell is intended for use at reactor-based neutron sources. The use of a large sample (1.5 cm3) allows rapid data collection. There are no major geometrical restrictions in the scattering plane. The projected temperature could be reached simultaneously to the application of pressure. First neutron experiments revealed a good signal-to-noise ratio of the diffracted neutrons. For the present layout of the Ti/Zr pressure cylinders and upper stability limit of 1.2 GPa was determined.

A heatable large volume high pressure cell for neutron powder diffraction: The Kiel-Berlin Cell I

A strengthened pressure cylinder for piston/cylinder devices is presented for use in angle-dispersive high-pressure neutron powder diffraction. It is shown that these cylinders, manufactured from Ti52/Zr48 zero-scattering alloy and strengthened by the shrink-fit method, allow the extension of the accessible pressure range of the Kiel–Berlin Cell I to 22 kbar.

A strengthened zero-scattering-alloy pressure cylinder for neutron powder diffraction

A heatable high-pressure neutron powder diffraction cell has been developed on the basis of the well-known McWhan piston-cylinder typw. It operates up to 700K and 15 kbar, simultaneously. The cell has successfully been applied for the investigation of phase diagrams as well as for standard high-pressure work. In order to extend the accessible range of pressure and temperature, a new cell has been designed. We hope to attain at least 35 kbar and 700-1000 K with this new cell.

B. Annighöfer

Papers

A heatable large volume high pressure cell for neutron powder diffraction: The Kiel-Berlin Cell I

A strengthened zero-scattering-alloy pressure cylinder for neutron powder diffraction

The Kiel/Berlin high-pressure cells for neutron powder diffraction