Angle-dispersive x-ray-diffraction and x-ray-absorption near-edge structure measurements have been performed on ${\mathrm{CaWO}}_4$ and ${\mathrm{SrWO}}_4$ up to pressures of approximately 20 GPa. Both materials display similar behavior in the range of pressures investigated in our experiments. As in the previously reported case of ${\mathrm{CaWO}}_4$, under hydrostatic conditions ${\mathrm{SrWO}}_4$ undergoes a pressure-induced scheelite-to-fergusonite transition around 10 GPa. Our experimental results are compared to those found in the literature and are further supported by ab initio total-energy calculations, from which we also predict the instability at larger pressures of the fergusonite phases against an orthorhombic structure with space group Cmca. Finally, a linear relationship between the charge density in the $A{\mathrm{O}}_8$ polyhedra of $AB{\mathrm{O}}_4$ scheelite-related structures and their bulk modulus is discussed and used to predict the bulk modulus of other materials, like hafnon.

The melting curve of Mg, Mn, Cu, Ag, Au, Zn, Cd, Al, In, and Pb has been measured up to 12 GPa using a Bridgman-type cell. Melting at high-pressure was identified detecting discontinuities in the electrical resistance of the studied metals. The results are compared with previous experimental and theoretical studies when possible. A comparison with the Lindemann’s law predictions is also done. In particular we found that among the studied metals Pb has the steepest melting curve (dTM/dP=78 K/GPa). In contrast, Mn has the flattest melting curve (dTM/dP=29 K/GPa). The reported results suggest that the electronic structure of an element might play a key role in determining the pressure dependence of its melting curve.

Current interest in barocaloric effects has been stimulated by the discovery that these pressure-driven thermal changes can be giant near ferroic phase transitions in materials that display magnetic or electrical order. Here we demonstrate giant inverse barocaloric effects in the solid electrolyte AgI, near its superionic phase transition at ~420 K. Over a wide range of temperatures, hydrostatic pressure changes of 2.5 kbar yield large and reversible barocaloric effects, resulting in large values of refrigerant capacity. Moreover, the peak values of isothermal entropy change (60 J K⁻¹ kg⁻¹ or 0.34 J K⁻¹ cm⁻³) and adiabatic temperature changes (18 K), which we identify for a starting temperature of 390 K, exceed all values previously recorded for barocaloric materials. Our work should therefore inspire the study of barocaloric effects in a wide range of solid electrolytes, as well as the parallel development of cooling devices.

Room-temperature angle-dispersive x-ray diffraction measurements on zircon-type YPO4 and ErPO4, and monazite-type GdPO4, EuPO4, NdPO4, and LaPO4 were performed in a diamond-anvil cell up to 30 GPa using neon as pressure-transmitting medium. In the zircon-structured oxides we found evidence of a reversible pressure-induced structural phase transformation from zircon to a monazite-type structure. The onset of the transition is at 19.7 GPa in YPO4 and 17.3 GPa in ErPO4. In LaPO4 a nonreversible transition is found at 26.1 GPa and a barite-type structure is proposed for the high-pressure phase. For the other three monazites studied, their structures were found to be stable up to 30 GPa. Evidence for additional phase transitions or chemical decomposition of the materials was not found in the experiments. The equations of state and axial compressibility for the different phases are also determined. In particular, we found that in a given compound the monazite structure is less compressible than the zircon structure. This fact is attributed to the higher packing efficiency of monazite versus zircon. The differential bond compressibility of different polyhedra is also reported and related to the anisotropic compressibility of both structures. Finally, the sequence of structural transitions and compressibilities are discussed in comparison with other orthophosphates.

In this work, the melting line of platinum has been characterized both experimentally, using synchrotron X-ray diffraction in laser-heated diamond-anvil cells, and theoretically, using ab initio simulations. In the investigated pressure and temperature range (pressure between 10 GPa and 110 GPa and temperature between 300 K and 4800 K), only the face-centered cubic phase of platinum has been observed. The melting points obtained with the two techniques are in good agreement. Furthermore, the obtained results agree and considerably extend the melting line previously obtained in large-volume devices and in one laser-heated diamond-anvil cells experiment, in which the speckle method was used as melting detection technique. The divergence between previous laser-heating experiments is resolved in favor of those experiments reporting the higher melting slope.