Crystal Structure of La6Mg4Ta2W2O24 Oxide: A Representative of a Novel A3nB'2n
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- 作者：Dmitry D. Khalyavin ; Augusto B. Lopes ; Ana M. R. Senos ; Pedro Q. Mantas
- 刊名：Chemistry of Materials
- 出版年：2006
- 出版时间：August 8, 2006
- 年：2006
- 卷：18
- 期：16
- 页码：3843 - 3849
- 全文大小：463K
- 年卷期：v.18,no.16(August 8, 2006)
- ISSN：1520-5002
文摘
The crystal structure of a new A-site deficient La6Mg4Ta2W2O24 perovskite oxide has been solved inthe space group I2/a (a = 7.8711(10) Å, b = 31.9057(10) Å, c = 7.8762(10) Å, and 
= 90.08(1)
)from X-ray powder diffraction data. The highest symmetry structural motif which does not involveoctahedral tilting is characterized by the Ibam space group and represents a sequence of [LaO], [Mg1/2(Ta/W)1/2O2], and [La1/2O] layers stacked along the b axis. The lanthanum ions and the vacancies in thelanthanum poor layers are ordered and form rows along the c direction. There are two types of theselayers which are shifted between each other in a half period along the a axis. The alternation of thelanthanum poor layers with the lanthanum rich ones, along with the rock salt type cation ordering betweenMg2+ and Ta5+/W6+, results in a 2ap × 8ap × 2ap type superstructure. An antiphase octahedral tiltingaround the b axis reduces the symmetry from orthorhombic Ibam to monoclinic I2/a. The number ofequivalent [La1/2O] layers, n, contained in a unit cell of the parent untilted crystal structure allows a newhomologous series, A3nB'2nB' '2nO12n, with the common Ibam space group and 2ap × 4nap × 2ap typesuperstructure to be identified. The La6Mg4Ta2W2O24 oxide is a representative with n = 2.
= 90.08(1))from X-ray powder diffraction data. The highest symmetry structural motif which does not involveoctahedral tilting is characterized by the Ibam space group and represents a sequence of [LaO], [Mg1/2(Ta/W)1/2O2], and [La1/2O] layers stacked along the b axis. The lanthanum ions and the vacancies in thelanthanum poor layers are ordered and form rows along the c direction. There are two types of theselayers which are shifted between each other in a half period along the a axis. The alternation of thelanthanum poor layers with the lanthanum rich ones, along with the rock salt type cation ordering betweenMg2+ and Ta5+/W6+, results in a 2ap × 8ap × 2ap type superstructure. An antiphase octahedral tiltingaround the b axis reduces the symmetry from orthorhombic Ibam to monoclinic I2/a. The number ofequivalent [La1/2O] layers, n, contained in a unit cell of the parent untilted crystal structure allows a newhomologous series, A3nB'2nB' '2nO12n, with the common Ibam space group and 2ap × 4nap × 2ap typesuperstructure to be identified. The La6Mg4Ta2W2O24 oxide is a representative with n = 2.