Synthesis and Characterization of New AA′BWO₆ Perovskites Exhibiting Simultaneous Ordering of A-Site and B-Site Cations

Six new AA ′ BB ′O 6 perovskites KLaMnWO 6, NaLaMnWO 6, NaNdMnWO 6, NaTbMnWO 6, NaNdCoWO 6, and NaNdMgWO 6 have been prepared. Each possesses the unusual combination of layered ordering of the A -site cations and rock-salt ordering of the B -site cations. The structure and properties of these samples have been characterized using monochromatic X-ray and neutron powder diffraction, UV–vis diffuse reflectance spectroscopy, and SQUID magnetometry. NaLaMnWO 6, NaNdMnWO 6, and NaTbMnWO 6 adopt a structure with monoclinic P 2 1 symmetry arising from the combination of cation ordering and a – a – c + octahedral tilting. The structures of the other three compounds are similar, but the presence of satellite reflections in the neutron diffraction data suggests a more complicated superstructure. Each of the four AA′ MnWO 6 samples shows a paramagnetic to antiferromagnetic transition with Néel temperatures ranging from 6 to 15 K. The NaTbMnWO 6 compound shows a second magnetic transition at ∼9 K. The origin of two magnetic phase transitions appears to arise from coupling between the Mn 2+ sublattice and the Tb 3+ sublattice.