Anomalous Thermal Expansion Of Mercurous Halides

Mercurous halides; mercurous iodide (Hg2I2), mercurous bromide (Hg2Br2) and mercurous chloride (Hg2Cl2) are high figure of merit materials for fabricating Acousto-optic (AO) devices that operate in the visible and infrared regions. Single crystals of mercurous halides were grown by physical vapor transport (PVT) method. Thermal expansion as well as the effect of annealing on the material are discussed. Mercurous halides show positive thermal expansion along "a" axis whereas no significant thermal expansion along "c" axis. The coefficients of thermal expansion of Hg2Cl2, Hg2Br2 and Hg2I2 are 6.72 x 10-5 degrees C-1, 6.44 x 10-5 degrees C-1 and 6.08 x 10-5 degrees C-1, respectively. The optical band gap of Hg2Cl2 was calculated using the transmission spectra as 2.9 eV.