Download citation
Download citation
link to html
A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 × 7.8 × 7.9 Å, which corresponds to a 12ap × 2ap × 2ap superstructure of the simple Pm\overline 3 m perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is aac0 with tilt angles of ∼ 8° about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6ap. Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768109032728/hw5005sup1.cif
Contains datablock global

txt

Text file https://doi.org/10.1107/S0108768109032728/hw5005sup2.txt
CIF of model structure

txt

Text file https://doi.org/10.1107/S0108768109032728/hw5005sup3.txt
Atomic coordinates and displacement parameters of model structure

txt

Text file https://doi.org/10.1107/S0108768109032728/hw5005sup4.txt
Atomic coordinates and displacement parameters of model structure

Computing details top

(global) top
Crystal data top
a = Åα = °
b = Åβ = °
c = Åγ = °
Data collection top
h = l =
k =
 

Follow Acta Cryst. B
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds