Cation Ordering in (NaLa)(MgW)O6 with the Perovskite Structure

Abstract

The title compound with an ordered monoclinic (pseudotetragonal) perovskite structure has been prepared. The lattice constants are a=5.5239(5), b=5.5253(4), c=7.8936(6) Å, β=90.16(1)°, and Z=2. The superstructure was found to be due to a layer-like ordering of Na+ and La3+ ions along alternate c-planes as well as a NaCl-type ordering of Mg2+ and W6+ ions in the octahedral sites. This new compound is the first example for the occurence of cation ordering in the A site. The origin of the superstructure was discussed.

Crystal Structure and Phase Transition in the Defect Pyrochlore NH4NbWO6

“…This nonphysical value could result from a particular arrangement of W/Nb cations in the B O sublattice, as commonly found in ABO perovskites in which the B site is occupied by cations of different size and charge (39).…”

A-site cation ordering in AA′BB′O6 perovskites

“…2. Our initial attempts to analyze the X-ray powder data were carried out with a P2 1 =m starting model, as this was the space group assignment by Sekiya et al [24] and subsequently Arillo et al [32]. While the assignment to the space group P2 1 =m is consistent with the distortion a À a À c 0 in Fig.…”

“…Another example is the partial ordering of Nd 3+ and Ag + , observed in NdAgTi 2 O 6 samples prepared under high-pressure conditions [22]. In 1984 Sekiya et al published the structure of NaLaMgWO 6 [24]. This compound is reported to exhibit both rock salt ordering of the B-site cations and layered ordering of the A-site cations.…”

Empirical Evidence for A‐Site Order in Perovskites

“…). For example, (NaLa)(MgW)O 6 forms in tetragonal P 4 /mmm and orders with a layered geometry while (CaFe)Ti 2 O 6 forms in tetragonal P 4 2 /nmc and orders with a columnar geometry, and (NaBa)(LiNi)F 6 forms in cubic , ordering with a rock‐salt geometry . Other geometries are possible for different stoichiometries.…”