Structural Characterization of New Layered Perovskites MLa2Ti2TaO10 (M=Cs, Rb) and NaLa2Ti2TaO10 ·xH2O (x=2, 0.9, 0)

✍ Scribed by Young-Sik Hong; Chi-Hwan Han; Keon Kim

• Book ID: 102974944
• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 556 KB
• Volume: 158
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9109

✦ Synopsis

The crystal structures of n ‫؍‬ 3 Dion+Jacobson phases MLa 2 Ti 2 TaO 10 (M ‫؍‬ Cs, Rb) and NaLa 2 Ti 2 TaO 10 ' xH 2 O (x ‫؍‬ 2, 0.9, 0) have been investigated by the Rietveld analysis of their powder XRD patterns. These compounds show the newtype ordering sequence of (Ti 1/2 Ta 1/2 )O 6 +TiO 6 +(Ti 1/2 Ta 1/2 )O 6 in the tripled octahedra, corresponding to the niobium analogs of MLa 2 Ti 2 NbO 10 . They crystallize in the tetragonal system P4/mmm with lattice constants of a ‫؍‬ 3.84733(9) and c ‫؍‬ 15.4364(4) A s for CsLa 2 Ti 2 TaO 10 , and a ‫؍‬ 3.8342(2) and c ‫؍‬ 15.2776(9) A s for RbLa 2 Ti 2 TaO 10 . Sodium-exchanged phase was easily hydrated to NaLa 2 Ti 2 TaO 10 ' 2H 2 O, belonging to the space group I4/mmm with a ‫؍‬ 3.8399(3) and c ‫؍‬ 34.288(3) A s . Upon 5ring, NaLa 2 Ti 2 TaO 10 ' 2H 2 O was dehydrated to NaLa 2 Ti 2 TaO 10 ' 0.9H 2 O with P4/mmm at around 1003C and then NaLa 2 Ti 2 TaO 10 with I4/mmm at above 2003C. The Na cations in two hydrates were surrounded with six oxygens, forming face-shared octahedra along (110) direction. These structural models, especially for the coordination environment of Na cations, were proposed for the 5rst time.