K2Ta4O11 (“kalitantite”): a wide band gap semiconductor synthesized in molybdate flux medium

Abstract

The successful application of molybdate flux for the crystal growth of complex tantalum oxide, verbi causa kalitantite, was shown at a submillimetre scale. The structure was determined via X-ray single crystal refinements (space group Rc, a = 627.32(2) pm, c = 3685.75(13) pm, V = 1256.11(7) pm³ × 10⁻⁶, Z = 6) to be an α-U₃O₈-type layered compound presenting the general formula M_x(Nb,Ta)_3n+1O_8n+3 (where n = 1 in the case of M being Na, Ca or Ag and n = 2 when M is La–Eu, Y or Bi), thus corroborating earlier studies. Experimental evaluations and complementary ab initio calculations revealed the semiconductor nature of K₂Ta₄O₁₁. The former were used to explain the vibrational spectrum in the mid-infrared range of wavenumbers.