[show abstract][hide abstract] ABSTRACT: 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 P2 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.
Chemistry of Materials 12/2007; · 8.24 Impact Factor