Characterization of the piezochromic behavior of some members of the CuMo1-xWxO4 series.
The members of the CuMo(1- x)WxO4 series (0 < or = x < 0.1) undergo a first-order phase transition that can be induced by pressure application; the thermochromic properties of such a series have already been reported. The two polymorphic forms exhibit two distinguishable colors: green for the low pressure form (alpha) and brownish-red for the high pressure one (gamma). These oxides can open up a new market for friendly pressure indicators, particularly for the compositions (0.07 < or = x < or = 0.1) for which the two polymorphs are stable at room temperature, that is, for which the color transition via pressure application is nonreversible. Within the CuMo(1- x)WxO4 solid solution domain, the dependence of the transition pressure versus tungsten content, temperature of measurement, and sample thermal-pressure history was studied. A large control of the transition pressure (from 5 to several 100 MPa) was brought to the fore. The transition was then studied using X-ray diffraction and transmission electron microscopy-energy dispersive X-ray analyses. This first-order transition, occurring by atomic migration inside the cell, seems to be preceded by an atomic disordering; moreover, transition temperatures may be modified by W segregation at the surface of the grains.
Gaudon
M
M
Institut de Chimie de Matière Condensée de Bordeaux, 87 Avenue du Docteur Schweitzer, 33608 PESSAC Cedex, France. gaudon@icmcb-bordeaux.cnrs.fr
Thiry
A E
AE
Largeteau
A
A
Deniard
P
P
Jobic
S
S
Majimel
J
J
Demourgues
A
A