On the lamellar compounds CuBiP(2)Se(6), AgBiP(2)Se(6) and AgBiP(2)S(6). Antiferroelectric phase transitions due to cooperative Cu(+) and Bi(3+) ion motion.

CuBiP(2)Se(6), AgBiP(2)Se(6), and AgBiP(2)S(6) were prepared from the corresponding elements. CuBiP(2)Se(6) and AgBiP(2)Se(6) crystallize in the space group R with a = 6.5532(16) A and c = 39.762(13) A for CuBiP(2)Se(6) and a = 6.6524(13) A and c = 39.615(15) A for AgBiP(2)Se(6). AgBiP(2)S(6) crystallizes in the triclinic space group P with a = 6.3833(13) A, b = 7.1439(14) A, c = 9.5366(19) A, alpha = 91.89(3) degrees , beta = 91.45(3) degrees , gamma = 94.05(3) degrees . CuBiP(2)Se(6) was found to exhibit a temperature-dependent antiferroelectric ordering of the Cu(+) and Bi(3+) ions in the lattice. An intermediate and a fully ordered structure were refined at 173 and 97 K, respectively. Electronic band and total energy calculations at the DFT level clearly suggest that the antiferroelectric model is energetically favored over the paraelectric and hypothetical ferrielectric models. This phase transition can be classified as a second-order Jahn-Teller distortion. The antiferroelectric state of CuBiP(2)Se(6) is an indirect gap semiconductor. The compounds were characterized with differential thermal analysis and solid-state UV/vis diffuse reflectance spectroscopy. Generalized implications regarding the expected ferroelectric behavior of compounds in the CuMP(2)Se(6) system (M = trivalent metal) are discussed.