High-pressure X-ray science on the ultimate storage ring

High-Pressure Phase Transformations in TiPO4 : A Route to Pentacoordinated Phosphorus

Titanium(III) phosphate, TiPO₄  , is a typical example of an oxyphosphorus compound containing covalent P-O bonds. Single-crystal X-ray diffraction studies of TiPO₄ reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high-pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO₄ -V is the first inorganic phosphorus-containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO₄ -V coexists with TiPO₄ -IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO₄ -II is found to be an incommensurately modulated phase whereas a lock-in transition at about 7 GPa leads to TiPO₄ -III with a fourfold superstructure compared to the structure of TiPO₄ -I at ambient conditions. TiPO₄ -II and TiPO₄ -III are similar to the corresponding low-temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin-Peierls interactions.

Diffraction-limited storage rings - a window to the science of tomorrow

This article summarizes the contributions in this special issue on Diffraction-Limited Storage Rings. It analyses the progress in accelerator technology enabling a significant increase in brightness and coherent fraction of the X-ray light provided by storage rings. With MAX IV and Sirius there are two facilities under construction that already exploit these advantages. Several other projects are in the design stage and these will probably enhance the performance further. To translate the progress in light source quality into new science requires similar progress in aspects such as optics, beamline technology, detectors and data analysis. The quality of new science will be limited by the weakest component in this value chain. Breakthroughs can be expected in high-resolution imaging, microscopy and spectroscopy. These techniques are relevant for many fields of science; for example, for the fundamental understanding of the properties of correlated electron materials, the development and characterization of materials for data and energy storage, environmental applications and bio-medicine.