title: Defect structure, phase separation, and electrical properties of nonstoichiometric tetragonal tungsten bronze Ba(0.5-x)TaO(3-x).
abstract: New insight into the defect chemistry of the tetragonal tungsten bronze (TTB) Ba(0.5-x)TaO(3-x) is established here, which is shown to adapt to a continuous and extensive range of both cationic and anionic defect stoichiometries. The highly nonstoichiometric TTB Ba(0.5-x)TaO(3-x) (x = 0.25-0.325) compositions are stabilized via the interpolation of Ba(2+) cations and (TaO)(3+) groups into pentagonal tunnels, forming distinct Ba chains and alternate Ta-O rows in the pentagonal tunnels along the c axis. The slightly nonstoichiometric Ba(0.5-x)TaO(3-x) (x = 0-0.1) compositions incorporate framework oxygen and tunnel cation deficiencies in the TTB structure. These two mechanisms result in phase separation within the 0.1< x < 0.25 nonstoichiometric range, resulting in two closely related (TaO)(3+)-containing and (TaO)(3+)-free TTB phases. The highly nonstoichiometric (TaO)(3+)-containing phase exhibits Ba(2+) cationic migration. The incorporation of (TaO)(3+) units into the pentagonal tunnel and the local relaxation of the octahedral framework around the (TaO)(3+) units are revealed by diffraction data analysis and are shown to affect the transport and polarization properties of these compositions.
authors.affiliation: Guangxi Ministry-Province Jointly-Constructed Cultivation Base for State Key Laboratory of Processing for Nonferrous Metal and Featured Materials, MOE Key Laboratory of New Processing Technology for Nonferrous Metals and Materials, College of Materials Science and Engineering, Guilin University of Technology , Guilin 541004 People's Republic of China.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Kuang
authors.forename: Fengjuan
authors.initials: F
authors.lastname: Pan
authors.forename: Jiang
authors.initials: J
authors.lastname: Cao
authors.forename: Chaolun
authors.initials: C
authors.lastname: Liang
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Suchomel
authors.forename: Florence
authors.initials: F
authors.lastname: Porcher
authors.forename: Mathieu
authors.initials: M
authors.lastname: Allix