Structure Change via Partial Se/Te Substitution: Crystal Structure and Physical Properties of the Telluride Ba<sub>2</sub>Cu<sub>4−<i>x</i></sub>Te<sub>5</sub> in Contrast to the Selenide-Telluride Ba<sub>2</sub>Cu<sub>4−<i>x</i></sub>Se<sub><i>y</i></sub>Te<sub>5−<i>y</i></sub>
收藏资源简介：
The chalcogenides Ba2Cu4−xSeyTe5−y were synthesized from the elements in stoichiometric ratios at 700 °C, followed by annealing at 600 °C. The ternary telluride Ba2Cu4−xTe5 crystallizes in a new structure type, space group C2/c, with lattice dimensions of a = 9.4428(6) Å, b = 9.3289(6) Å, c = 13.3028(8) Å, β = 101.635(1)°, V = 1147.8(1) Å3, for x = 0.75(1) (Z = 4). The corresponding selenide-telluride adopts another new, but strongly related, structure type, space group P41212, with a = 6.5418(3) Å, c = 25.782(2) Å, V = 1103.3(1) Å3, for Ba2Cu3.26(2)Se0.729(8)Te4.271 (Z = 4). Between 0.13 and 1.0 Te per formula unit can be replaced with Se, while the Cu content appears to vary only within 0.67 ≤ x ≤ 0.81 for Ba2Cu4−xSeyTe5−y. Despite crystallizing in different crystal systems, the telluride and the selenide-telluride exhibit topologically equivalent structure motifs, namely, chains of Cu(Se,Te)4 tetrahedra with a Cu atom cis/trans chain as well as an almost linear Te atom chain. All these chalcogenides, as far as measured, are p-doped semiconductors, as determined by Seebeck coefficient and electrical conductivity measurements.
