Determination of thermal expansion of KCaI3 using in-situ high temperature powder X-ray diffraction

KCaI3:Eu single crystals exhibit favorable scintillation properties and have potential for use in domestic security applications requiring radioisotope identification. The anisotropic thermal expansion of the orthorhombic unit cell of this perovskite-type scintillator has been investigated using in-situ high temperature X-ray diffraction on powdered samples. Samples from single crystals of both pure and Eu-doped KCaI3 grown by the Bridgman method were used for comparison. Expansion with temperature along the b-axis is greatest with an average linear coefficient of thermal expansion of ≈ (41-46) x 10−6 K−1 resulting from the weaker bonding between alternating layers of K and Ca parallel to the b-axis. Thermal expansion in each of the KCaI3 samples has the highest degree of anisotropy with respect to the b and c axis with ratio ᾱb/ᾱc of 1.4-1.5. Additionally, we identify the predominant cleavage plane in KCaI3 as (0 -3 -1) based upon Laue reflection imaging.