A double-walled sapphire single-crystal gas-pressure cell (type III) for in situ neutron diffraction.

In situ neutron diffraction is an important characterization technique for the investigation of many functional materials, e.g. for hydrogen uptake and release in hydrogen storage materials. A new sapphire single-crystal gas-pressure cell for elastic neutron scattering has been developed and evaluated; it allows conditions of 298 K and 9.5 MPa hydrogen pressure and 1110 K at ambient pressure. The pressure vessel consists of a sapphire single-crystal tube of 35 mm radius and a sapphire single-crystal crucible as sample holder. Heating is realized by two 100 W diode lasers. It is optimized for the D20 diffractometer, ILL, Grenoble, France, and requires the use of a radial oscillating collimator. Its advantages over earlier sapphire single-crystal gas-pressure cells are higher maximum temperatures and lower background at low and high diffraction angles. The deuterium uptake in palladium was followed in situ for validation, proving the potential of the type-III gas-pressure cell for in situ neutron diffraction on solid-gas reactions.

Design and use of a sapphire single-crystal gas-pressure cell for in situ neutron powder diffraction.

A sapphire single-crystal gas-pressure cell without external support allowing unobstructed optical access by neutrons has been developed and optimized for elastic in situ neutron powder diffraction using hydrogen (deuterium) gas at the high-intensity two-axis diffractometer D20 at the Institut Laue-Langevin (Grenoble, France). Given a proper orientation of the single-crystal sample holder with respect to the detector, parasitic reflections from the sample holder can be avoided and the background can be kept low. Hydrogen (deuterium) gas pressures of up to 16.0 MPa at 298 K and 8.0 MPa at 655 K were tested successfully for a wall thickness of 3 mm. Heating was achieved by a two-sided laser heating system. The typical time resolution of in situ investigations of the reaction pathway of hydrogen (deuterium) uptake or release is on the order of 1 min. Detailed descriptions of all parts of the sapphire single-crystal gas-pressure cell are given, including materials information, technical drawings and instructions for use.

LiSr2SiO4H, an Air-Stable Hydride as Host for Eu(II) Luminescence.

LiSr2SiO4H is synthesized by solid-state reaction of LiH and α-Sr2SiO4. It crystallizes in space group P21/ m ( a = 658.63(4) pm, b = 542.36(3) pm, c = 695.01(4) pm, ß = 112.5637(9)°) as proven by X-ray and neutron diffraction, is isotypic to LiSr2SiO4F, and exhibits isolated SiO4 tetrahedra. Hydride anions are located in Li2Sr4 octahedra, which share faces to form columns, with H-H distances of 271.18(2) pm. NMR, IR, and Raman spectroscopy, density measurements, elemental analysis, and theoretical calculations confirm these results. Despite its hydridic nature, it is stable in air up to 550 K. When doped with europium, it emits bright yellow-green light with an intensity maximum at 560 nm for LiSr1.98Eu0.02SiO4H. Even after treatment in water for several hours, the solid shows luminescence. The broad emission peak is attributed to the allowed 4f65d → 4f7 transition of divalent europium. LiSr2SiO4H is the first silicate hydride, a class of compounds that might have potential as host for luminescent materials.