La_8+xTi_8+yS₂₄O₄ Compounds Where x + y ≤ 2:  A Series of Phases with Mixed-Valent Titanium

Abstract

O 4 , were prepared by high-temperature methods (1025-1050 °C; ∼80-150 h) from La 2 S 3 , Ti, S, and either La 2 O 3 or TiO 2 as oxygen sources. LaCl 3 (∼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 ∞ 2 [(Ti 4 S 2 O 4 )(Ti-S 6 ) 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 La 8+x Ti 8+y S 24 O 4 , where (x + y) e 2 and the oxidation states of Ti can vary from +3 to +4. Crystal data (153 K) of La 8.75 Ti 9.25 S 24 O 4 : tetragonal space group P4/mmm, a ) 10.4205(8) Å, c ) 8.3848(6) Å, V ) 910.5(1) Å 3 , Z ) 1, R(F) ) 3.88% and wR(F 2 ) ) 7.22%. For La 8.50 Ti 9.50 S 24 O 4 , tetragonal space group P4/mmm, a ) 10.4101(3) Å, c ) 8.396(1) Å, V ) 909.9(1) Å 3 , Z ) 1, R(F) ) 3.54% and wR(F 2 ) ) 8.16%. For La 8.10 Ti 8.05 S 24 O 4 , tetragonal space group P4/mmm, a ) 10.4212(3) Å, c ) 8.233(2) Å, V ) 894.1(2) Å 3 , Z ) 1, R(F) ) 4.25% and wR(F 2 ) ) 11.12%.

Syntheses and Crystal Structures of the Lanthanum Titanium Oxyselenides La4Ti2O4Se5 and La6Ti3O5Se9

“…The question is whether these di!erently charged cations are ordered on speci"c sites or disordered over all Ti sites. Recently several mixed-valence rare-earth titanium oxychalcogenides have been reported (2,5,6,11), but in none was a precise assignment of Ti> and Ti> sites made. Such assignments are made di$cult by the tendency of both Ti> and Ti> to be in an octahedral environment and by the small di!erence in their ionic radii (12).…”

“…Invariably the oxidation state¸n(#III) can be assigned, leaving only the question of the formal oxidation state of Ti, either Ti(#III) or Ti(#IV) or both. Among these compounds, some have been classi"ed as mixed-valence compounds (2,5,6) Crystallography X-ray di!raction data were collected on a Bruker Smart 1000 CCD di!ractometer at 153 K with the use of monochromatized MoK radiation ( "0.71073 A > ). The di!racted intensities generated by a scan of 0.33 in were recorded on multiple sets of 606 frames covering more than a hemisphere of the Ewald sphere.…”

“…site. Subsequent re"nements, including unconstrained occupancies for the newly introduced positions, led to improved (1)}Se (2) 95.4(1) Se (4)}Ti (2)}Se (6) 92.48(8) Se(2)}Ti(1)}Se (2) 96.83(5) Se(6)}Ti(2)}Se(6) 75.0(2) O(2)}Ti(1)}Se (1) 87.5(1) O(5)}Ti(2)}Se(7) 89.9(2) Se(2)}Ti(1)}Se (1) 175.62(6) Se(6)}Ti(2)}Se (7) 174.5(1) Se(2)}Ti(1)}Se (1) 86.46(1) O(2)}Ti(1)}Se (1) 87.5(1) Se(1)}Ti (1)}Se (1) 90.10 (5) Ti (3)}O (1) (1)}Se (4) 92.14(14) Se (3)}Ti (2)}Se (3) 98.19(6) O(3)}Ti (1)}Se (4) 92.29 (14) O (5)}Ti (2)}Se (7) 170.9(2) Se(4)}Ti (1)}Se (4) 95.61 (6) Se (3)}Ti (2)}Se (7) 89.84(5) O(2)}Ti (1)}Se (8) 87.91 (14) O (5)}Ti (2)}Se (2) 90.65(15) O(3)}Ti (1)}Se (8) 87.59 (14) Se (3)}Ti (2)}Se (2) 83.34(2) Se(4)}Ti (1)}Se (8) 179.25(6) Se (3)}Ti (2)}Se (2) 172.88(8) Se (4)}Ti (1)}Se (8) 85.14(2) Se …”

Synthesis and Structural Analysis of Bi0.5La13.5Ti8S29Cl4O4 and La23.1Ti16.2S49Cl8O8: Two New Oxychlorosulfide Compounds with 2∞[(Ti4Q2O4)(TiQ6)4/2] Layers Where Q=S/Cl

“…Atom S(18) was also found to lie approximately 0.880 A s from itself and input at half occupancy. Ti (8) was also partially occupied with occupancy of 0.06974 where full site occupancy would be 0.25. All atoms, except for the La(7)/Ti(7a)/Ti(7b) and O(2) sites, were …”

“…With relatively high oxide concentrations (i.e., O:S'0. 5 (4,5,7,8). At very low oxygen concentration, the compound Ba Ti S O has been prepared (O:S"0.07) and shown to adopt a BaTiS -related structure (11).…”