We have carried out optical-absorption and reflectance measurements at room temperature in single crystals of AWO 4 tungstates (A = Ba, Ca, Cd, Cu, Pb, Sr, and Zn).

When monoclinic monazite-type LaVO 4 (space group P2 1 /n) is squeezed up to ∼12 GPa at room temperature, a phase transition to another monoclinic phase has been found. The structure of the high-pressure phase of LaVO 4 is indexed with the same space group (P2 1 /n), but with a larger unit-cell in which the number of atoms is doubled. The transition leads to an 8% increase in the density of LaVO 4 . The occurrence of such a transition has been determined by x-ray diffraction, Raman spectroscopy, and ab initio calculations. The combination of the three techniques allows us to also characterize accurately the pressure evolution of unit-cell parameters and the Raman (and IR)-active phonons of the low-and high-pressure phase. In particular, roomtemperature equations of state have been determined. The changes driven by pressure in the crystal structure induce sharp modifications in the color of LaVO 4 crystals, suggesting that behind the monoclinic-to-monoclinic transition there are important changes of the electronic properties of LaVO 4 . † Corresponding author, email: daniel.errandonea@uv.es † † Present address:

A pressure-induced phase transition, associated with an increase of the coordination number of In and Ta, is detected beyond 13 GPa in InTaO 4 by combining synchrotron x-ray diffraction and Raman measurements in a diamond-anvil cell with ab initio calculations. High-pressure optical-absorption measurements were also carried out. The high-pressure phase has a monoclinic structure that shares the same space group with the low-pressure phase (P 2/c). The structure of the high-pressure phase can be considered as a slight distortion of an orthorhombic structure described by space group Pcna. The phase transition occurs together with a unit-cell volume collapse and an electronic band-gap collapse observed by experiments and calculations. Additionally, a band crossing is found to occur in the low-pressure phase near 7 GPa. The pressure dependence of all the Raman-active modes is reported for both phases as well as the pressure dependence of unit-cell parameters and the equations of state. Calculations also provide information on infrared-active phonons and bond distances. These findings provide insights into the effects of pressure on the physical properties of InTaO 4 .

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A combined high-pressure experimental and theoretical study of the electronic band-structure of scheelite-type AWO4 (A=Ca, Sr, Ba, Pb) compoundsThe pressure behavior of the absorption edge of PbWO 4 was studied up to 15.3 GPa. It redshifts at −71 meV/ GPa below 6.1 GPa, but at 6.3 GPa the band gap collapses from 3.5 to 2.75 eV. From 6.3 to 11.1 GPa, the absorption edge moves with a pressure coefficient of −98 meV/ GPa, undergoing additional changes at 12.2 GPa. The results are discussed in terms of the electronic structure of PbWO 4 which attribute the behavior of the band gap to changes in the local atomic structure. The changes observed at 6.3 and 12.2 GPa are attributed to phase transitions.