La8+ x Ti8+ y S24O4 Compounds Where x + y ≤ 2:  A Series of Phases with Mixed-Valent Titanium

• Published in: Chemistry of materials 1998-08, Vol.10 (8), p.2078-2085
• Main Authors: Tranchitella, Louis J, Fettinger, James C, Heller-Zeisler, Susan F, Eichhorn, Bryan W
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm970663o

Three new titanium oxysulfides, La8.75Ti9.25S24O4, La8.50Ti9.50S24O4, and La8.10Ti8.05S24O4, were prepared by high-temperature methods (1025−1050 °C; ∼80−150 h) from La2S3, Ti, S, and either La2O3 or TiO2 as oxygen sources. LaCl3 (∼10−30 wt %) was added as a flux. The compounds were characterized by single-crystal X-ray diffraction, neutron activation analysis, and EDX analysis. All three compounds contain common [(Ti4S2O4)(TiS6)4/2](12+δ)- oxysulfide layers and disordered/variable composition titanium sulfide layers that alternately stack along the c-axis of the unit cell. The titanium sulfide layers contain extensive La/Ti solid solution formation and are characterized by 5-fold disorders at the M(2) octahedral sites and 2-fold disorders at the M(3) sites. These compounds are members of a series of compounds with the general formula La8+ x Ti8+ y S24O4, where (x + y) ≤ 2 and the oxidation states of Ti can vary from +3 to +4. Crystal data (153 K) of La8.75Ti9.25S24O4:  tetragonal space group P4/mmm, a = 10.4205(8) Å, c = 8.3848(6) Å, V = 910.5(1) Å3, Z = 1, R(F) = 3.88% and wR(F 2 ) = 7.22%. For La8.50Ti9.50S24O4, tetragonal space group P4/mmm, a = 10.4101(3) Å, c = 8.396(1) Å, V = 909.9(1) Å3, Z = 1, R(F) = 3.54% and wR(F 2 ) = 8.16%. For La8.10Ti8.05S24O4, tetragonal space group P4/mmm, a = 10.4212(3) Å, c = 8.233(2) Å, V = 894.1(2) Å3, Z = 1, R(F) = 4.25% and wR(F 2 ) = 11.12%.