New layered vanadium oxychalcogenides Nicola Kelly, Simon J. Clarke University of Oxford, UK
Layered cuprates such as YBa 2 Cu 3 O 7- x exhibit unconventional high-temperature superconductivity as a result of the CuO 2 square planes within their crystal structures. Recently, superconductivity has been discovered in the oxypnictides BaTi 2 Bi 2 O and BaTi 2 Sb 2 O which contain “anti-CuO 2 ” transition metal-oxide square layers, i.e. Ti 2 O [1]. Doping of these materials on the Ba site enhances T c [1], which led researchers to investigate other ways to apply chemical pressure to these systems. As such, three vanadium oxychalcogenides containing a V 2 O square net were reported, with the general formula A V 2 Ch 2 O where A is Rb or Cs and Ch is S, Se or Te, Fig. 1 [2-4]. The materials contain vanadium of intermediate valency on a single crystallographic site, producing metallic conductivity and temperature-independent paramagnetism. Here we report the synthesis and characterisation of six further compounds in this structural family, extending it to include A = K for the first time, Fig. 2 .
Fig. 1. Crystal structure of AV2Ch2O oxychalcogenides, space group P4/mmm. The V2O square net is the anti-type of the CuO2 planes in high-temperature superconductors.
Fig. 2. Lattice parameters of AV2Ch2O as a function of A and Ch ionic radii. References 1. T. Yajima. Titanium Pnictide Oxide Superconductors. Condens . Matter 2 , 4 (2017)
2. H. Lin et al . Structure and physical properties of CsV 2 Se 2- x O and V 2 Se 2 O. Phys . Rev . B 98 , 075132 (2018) 3. M. Valldor et al . Bad-Metal-Layered Sulfide Oxide CsV 2 S 2 O. Eur . J . Inorg . Chem . 2016 , 23 (2016) 4. A. Ablimit et al . Weak metal-metal transition in the vanadium oxytelluride Rb 1−δ V 2 Te 2 O. Phys . Rev . B 97 , 214517 (2018)
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