Phase transitions in Mn(Mo_1−xW_x)O₄ oxides under the effect of high pressure and temperature

Abstract

Phone: þ33 (0)5 40 00 66 85, Fax: þ33 (0)5 40 00 27 61 ABO 4 compounds exhibit various phase transitions identified in the literature. The phase transitions between monoclinic a-C 2/m and wolframite P 2/c structures of Mn(Mo 1Àx W x )O 4 compounds, which can be induced by pressure or temperature, are studied on the basis of X-ray diffraction analyses. The large optical contrast associated with both these structures and Mo/W environments can be exploited to propose efficient piezochromic sensors (thanks to the monoclinic to wolframite transition vs. pressure) and thermal sensors (thanks to the reverse transformation), the thermochromic temperature being able to be tuned via the Mo/W ratio.A(Mo,W)O 4 phase diagram: from wolframite to monoclinic compounds (drawn from the updated Bastide's diagram from Errandonea and Manjo [9]).

A Brief Review of the Effects of Pressure on Wolframite-Type Oxides

“…Between the recent advances, the one that has likely had more influence in the field has been the structural solution of the different post-wolframite structures. The precise knowledge of the pressure structural stability of different wolframites and their HP structures has opened two new avenues to explore: (i) the study of the scintillating properties of the HP polymorphs by means of HP photoluminescence studies; (ii) the changes produced by this structural change on the magnetic properties of those wolframites with an open d outer shell like multiferroic MnWO 4 ; and (iii) the behavior under compression of wolframite alloys like MnW 1-x Mo x O 4 [56]; in particular, CdW 1-x Mo x O 4 whose end-members have either the wolframite or scheelite structure. For these biphasic alloy systems, their HP behavior is unpredictable [57].…”

Brief Review of the Effects of Pressure on Wolframite-Type Oxides

“…Between those advances, probably the one that has had more MnW1-xMoxO4 [56]; in particular, CdW1-xMoxO4 whose end-members have either the wolframite or scheelite structure. For these biphasic alloy systems their HP behavior is unpredictable [57].…”