Research on the thermal expansion of AgGa 1−x In x Se 2 single crystals

Thermal expansion coefficients of AgGa1−xInxSe2 (x = 0.2, 0.3, 0.4) single crystals have been measured in the range from 323K to 823K. The values of αa are positive and increase with temperature whereas the values of αc are negative and their absolute magnitudes increase with the increasing temperature for different x. With the increase of x, thermal expansion coefficients αa and αc both decrease numerically. The mean linear thermal expansion coefficient αL and the anisotropy of thermal expansion αη have been calculated, and they are also decreasing numerically with the increasing x. The slope of the straight line αhkl versus cos2ϕ decreases as x increases at 473K and 773K, respectively. According to the variation of thermal expansion coefficients, the relationship between the thermal expansion coefficient, bond length, and melting point of AgGa1−xInxSe2 satisfies the equation αL=0.021Tm−B(d−d0)3. In addition, the mechanism of thermal expansion variation has been discussed in terms of crystal structure, bond lengths, and thermal vibration of bonds in AgGa1−xInxSe2 single crystals.