Double perovskite structure

With small A cations for which t 1, the cubic structure becomes unstable because the 12-coordinate site is too large for the A cation. The structure adjusts the size of the 12-coordinate site by cooperatively tilting 

It has been realised that the extent of cation ordering is an important issue in the synthesis of double perovskites where both thermodynamic and kinetic considerations are involved.The degree of cation order is crucial for the occurrence of unique magnetic and electrical properties. For example, magnetoresistive properties of Sr2FeMo06 vary depending on the extent of ordering of Fe and 

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R642 K. Asai, Studies of Ferromagnetic Oxides with Ordered Double Perovskite Structure by Nuclear Probes , KURRI-KR, 2000, (KURRI-KR-49, Proceedings of the Specialist Research Meeting on New Developments in Solid State Physics with Probes of Radiations and Nuclei, 1999), 229... 

A novel system was introduced to the catalytic field by Matsuda et al. (1993). A solid of the general formula ALaNb207 is made up of the layer compound LaNb207 with double perovskite structure interleaved with A atoms. If the interlayer compound is water, they call the compound HLa2Nb707 to indicate the acidic character of this system. They report the results obtained when 1- and 2-butanol were reacted over this solid at temperatures between 453 and 623 K. The secondary alcohol was much more reactive, as expected for an acid catalyst. Consistent with this, no dehydrogenation product was formed when... 

Table 2.1 Phases with the rock-salt-type double perovskite structure...

Figure 2.1 The octahedral framework of the rock-salt ordered double perovskite structure. The A-site cations are omitted for clarity...

Figure 8.8 (a) The double perovskite structure, (b) The Brownmillerite structure. 

Figure 2.32 The relationship between the simple perovskite and B-site ordered double perovskite structures. The B magnetic lattice is f.c.c.

HMAFM in oxides with double perovskite structure was proposed by Warren Pickett for the first time in 1998. Band structure calculations based on local spin-density approximations (LSDA), predicted La2MnV06 double perovskite as a promising candidate for exhibiting HMAFM. The calculations were based on the assumption that both Mn and V ions are trivalent and more importantly, that the Mn (d ) occurs in a low spin configuration (t2g" Cg ). The band structure of La2MnVOg show that only the minority 2g bands of both V and Mn contribute to the DOS near the The antiparallel alignment of low spin Mn + (tzg Ttzg i) and states would yield a net zero... 

La2MnVOg, which is not an HMAFM due to the absence of complete B-site order and apparent presence of high-spin Mn and Considering the negUgible size difference between Mn (0.645 A) and (0.64 A), their ordering in the double perovskite structure is unexpected. Recently, it was shown that even with a more reduced Mn than... 

Ti,Nb)-0, and La-deficient La2-02 layers (Fig. 6.7(a)). Two-dimensional lithium cation conduction has also been reported in the orthorhombic layered perovskite-type compound Lao.62Lio.i6Ti03 [55], in which the Li cation exists and migrates only near the La-deficient La2-02 layer. This work has thus revealed that oxide ion diffusion in an ionic conductor with a double perovskite structure is two dimensional. 

Figure 2.22 Representation of the double perovskite structure adopted by the GdBaCo205. Gd atoms are shown as light grey spheres, Ba atoms are shown as dark grey spheres and Co atoms are located at the centre of the polyhedra...

Multiferroic materials with double-perovskite structure aA BB O ) are solid solutions of two perovskites ABO and [a B O3). In [aa BB oj, A and A represent alkaline rare earth cations (La, Y, and Ce), while B and B are transition metal cations (Ni and Co). If A and A represent the same chemical element, the double perovskite has the general formula (AjBB O ) and the crystal structure of A B B Og -type perovskite, as shown in Figure 2. Alkali-earth and lanthanide (smaller ion) ions are alone usually occupied in the A site [27,28]. If the A ion is too small, the common expected distortions are cation displacement with BOg and octahedral ones [29]. 

Fig. 14 Schematic representation of the double perovskite structure AA B205 5 where A Rare earth, A Alkaline earth,...

Q.J. Zhou, T.M. He, Y. Ji, SmBaCo205+x double-perovskite structure cathode material for intermediate-temperature solid-oxide fuel cells. J. Power Sources 185, 754—758 (2008)... 

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