New series of honeycomb ordered oxides, Na3M2SbO6 (M(ii) = Mn, Fe, (Mn, Fe), (Mn, Co)): synthesis, structure and magnetic properties.

New layered oxides, Na3M2SbO6 (M(ii) = Mn, Fe) have been synthesized by solid state reactions under inert conditions. Rietveld refinements of the powder X-ray diffraction measurements confirmed the structures in the C2/m space group. The layered structure consists of honeycomb slabs with ordered M2+ (Mn or Fe) and Sb5+ cations, separated by Na+ ions in the interlayer octahedral sites. X-ray photoelectron spectroscopy measurements further substantiated the presence of Mn2+, Fe2+ and Sb5+ ions. A paramagnetic behavior has been exhibited by Na3Mn2SbO6 in the range of 300-100 K with negative Weiss constant (θ = -144 K). Zero field cooled and field cooled values diverged below 50 K and without the indication of a long-range antiferromagnetic order down to 2 K. On the other hand, Na3Fe2SbO6 has been found to display two different transitions in the magnetic susceptibility measurements. A distinct cusp appeared around T∼ 120 K followed by the divergence between the zero field cooled and the field cooled values. The observation of antiferromagnetic ordering (TN∼ 7.5 K) suggested the magnetic frustration behavior arising out of the placement of Fe2+ ions in the triangular lattice of the honeycomb layers. Partial substitution of Mn2+ ions by Fe2+ and Co2+ ions has resulted in isostructural Na3MnFeSbO6 and Na3MnCoSbO6 under similar experimental conditions. Magnetic properties have been significantly modified by the coexistence of Mn2+ and Fe2+ ions in Na3MnFeSbO6. Co2+ substitution resulted in paramagnetic behavior with θ∼-8.4 K confirming thereby the competing antiferromagnetic interactions. The scope of the present work has been explored by carrying out the ion-exchange experiments of the sodium analogues using molten salt (LiNO3) to synthesize new Li3M2SbO6 (M = Mn, Fe) oxides.