Кристалічна будова та хімічний зв`язок у проміжних сполуках системи Ti2Se–In2Se3–"P2se4"

Abstract

Perspective compounds that are widely used in production of working elements for semiconductor IR and laser technology, thermal generation, solar power, are materials based on complex chalcogenide compounds. Special attention is paid to compounds of the M2P2Se6 type, derived from Sn2P2S6(Se6). Modification of the composition of M2P2Se6 type compounds by isovalent substitutions of the chalcogen S®Se, which form the sublattice of the anionic group [P2X6]4–, as well as Sn2+®Pb2+, heterovalent substitutions 2Sn2+®4M1+ (M1 – K+, Na+, Rb+, Tl+, Ag+, Cu+), 2Sn2+®M1++M23+ (M2 – In3+, Sb3+, Bi3+, Fe3+) leads to the formation of new structures with different structure of cation sublattice, which is accompanied by a change in crystal-chemical parameters. Study of physical-chemical interaction in the Tl2Se–In2Se3–“P2Se4” system showed that intermediate complex selenides which melts congruently In2Se3 (1192 К), TlInSe2 (1023 К), Tl4P2Se6 (758 К), In4(P2Se6)3 (880 К), TlInP2Se6 (875 К) form five quasi-binary eutectic type sections with formation of limited solid solution. Crystalstructure studies of complex chalcogenides of the Tl2Se–In2Se3–“P2Se4” system were carried out by a powder method. Refinement of the structural parameters of intermediate compounds was carried out by the Rietveld method. Crystal-chemical parameters of compounds in the Tl2Se– In2Se3–“P2Se4” system are: In2Se3 hexagonal, Р61, a=7.129, c=19.381 Å; Tl2Se tetragonal, Р/n, а=8,540; с=12,380 Å; TlInSe2 tetragonal, I4/mcm, a=8.064, c=6.833 Å; Tl4P2Se6 monoclinic, P121/c1, a=12.239, b=9.055, c=12.328 Å, b=98.83о; In4(P2Se6)3 trigonal, R3h, a=6.381, c=20.014; TlInP2Se6 triclinic, P-1(2), a=6.449, b=7.542, c=12.166 Å,a=100.72, b=93.63 о, g=113.32 о. The crystal-chemical analysis of the М2P2Se6 type compounds showed that in their structure anionic group of atoms [P2Se6]4– can be isolated in the form of two fused tetrahedron, a pair of P–P from Phosphorus atoms occupy octahedron voids between the planes of Selenium atoms, cations of atoms (Tl, In) occupy position between layers of atoms of anionic groups. In the transition of In4(P2Se6)3®TlInP2Se6®Tl4P2Se6 with a decrease in the total electronegativity of the atoms of the cationic group (an increase in the total number of cations atoms per anionic group [P2Se6]4–), there is a corresponding decrease in the interatomic distances between a pair of Phosphorus P–Р atoms from 3,082 Å®2,278 Å®2,217 Å, as well as the connections of P–Se 2,193¸2,233 Å® 2,184¸2,235 Å®2,100¸2,246 Å, indicating an increase in the stability of the anionic group [P2Se6]4–. For compound Tl4P2Se6 there is a discernible deformation of fused tetrahedron [P2Se6]4–. An analysis of crystal-chemical studies has shown that binary compounds characterized by a mixed type of chemical bond – ionic-covalent. Transition from binary compounds to complex compounds TlInSe2, TlInP2Se6, In4(P2Se6)3 and TlInP2Se6, due to trans-effects in the Tl–P–Se bonds system, increases the polarization of Tl–Se bonds, indicating an increase in contribution ionic component of chemical bonding. The opposite processes is observed for In–Se bonds, the polarization of which decreases, which leads to an increase in the power of the covalent component. An increase in the ion bond between cations of Tl+, In3+ and Se2– anionic groups also leads to decrease in the contribution of the metallic component in the ternary and quartery compounds to binary selenides. Keywords: selenodiphosphate; crystal structure; chemical bond.