Influence of the average atomic number of the A(2)TeC(6) and A(3)B(2)C(9) (A = K, Rb, Cs, Tl(I); B = Sb, Bi; C = Br, I) compounds on their melting point and band gap

We examine a correlation of the melting point (T (m)) and band gap Delta E of the A(2)TeC(6) and A(3)B(2)C(9) (A = K, Rb, Cs, Tl(I); B = Sb, Bi; C = Br, I) perovskite (ABC(3)) related halides with their average atomic number. The relationships found are interpreted in terms of the variation in the nature of chemical bonding in going from the K to Rb and Cs compounds and in terms of the key crystal-chemical features of these compounds. The results are used to predict the Delta E and T (m) of compounds that have not yet been synthesized and unexplored compounds.