Parametric diffraction with the high intensity neutron powder diffractometer D20 at ILL Grenoble, focussing on « energy » materials


For the inspection of processes involving condensed matter, in situ neutron powder diffraction proves itself to be a versatile tool, giving insight into processes of technological pertinence. Only a few high-intensity powder diffractometers at intense neutron sources allow for this. D20 at Institut Laue-Langevin provides the highest available intensity in constant wavelength neutron powder diffraction. A stationary, curved linear position sensitive detector allows for in-situ diffraction studies down to a second and encourages the use of complex sample environments with inherently small sample sizes. D20 adapts to various levels of crystallographic complexity and rapidity of an observed phenomenon.

Improvement of Li-ion battery electrode materials in terms of gravimetric and volumetric energy density, temperature operation range and cycling stability needs understanding of lithium (de)intercalation phenomena. In operando neutron diffraction techniques are well suited here. Electrochemical cells based on a neutron-transparent (Ti,Zr) alloy combine good electrochemical properties and the ability to collect neutron diffraction patterns with reasonable statistics and no other Bragg peaks than those of the electrode material. This allows detailed structural determination of electrode materials by Rietveld refinement in operation conditions.

Solid-oxide fuel cells convert chemical energy into electricity at higher efficiency than conventional methods, with less pollution. The anode must not alter at high temperature, not form nonconductive phases at interfaces and not degrade upon reduction and oxidation cycles. Single-phase mixed ionic and electronic conductors provide microstructural stability and increase the electrode fraction accessible to oxide ions. Many of those oxides have been investigated successfully in operando at high temperature under oxidizing and reducing gas flow by neutron diffraction, following the crystal chemistry of oxide ions during the process.

Classical in situ work (thermo-diffractometry) has been done on the photovoltaic materials, MaPbI3 and derivates, and neutron diffraction turned out to be a perfect tool to screen the crystal chemistry of light organic atoms beside the heavy metal atoms over a wide range of temperatures.

Hydrogen is an attractive energy carrier for renewable energy sources due to its high energy density. Solid-state hydrogen storage provides higher storage capacities than compressed or liquefied hydrogen. Complex metal hydrides have high hydrogen storage capacities but suffer from poor kinetic and thermodynamic properties. Neutron powder diffraction screens the crystal chemistry of the different phases in situ.

Last not least, the work on the structure and the formation and decomposition of gas hydrates and related ice phases shall be presented, as well as the prospects of neutron diffraction at very high pressures up to 25 GPa at low temperatures down to 1.6 K.