Dielectric permittivity of some novel copper/cobalt and rare-earth metal tungstates

Abstract

Abstract Polycrystalline samples of new copper and samarium tungstates (Cu 3 Sm 2 W 4 O 18 and CuSm 2 W 2 O 10 ) and cobalt and europium tungstate (CoEu 4 W 3 O 16 ) have been successfully synthesized by the solid state reaction of d -electron metal tungstates MWO 4 (M = Cu, Co) with corresponding rare-earth metal tungstate RE 2 WO 6 (RE = Sm and Eu). Broadband dielectric spectroscopy provides experimental evidence that in tungstates under study both relative dielectric permittivity ( ɛ r ) and loss tangent (tan δ ) strongly depend on the temperature and frequencies. Maximal relative permittivity value ɛ r = 42 for CuSm 2 W 2 O 10 , ɛ r = 30 for Cu 3 Sm 2 W 4 O 18 , and ɛ r = 63,000 for CoEu 4 W 3 O 16 at low frequency ( ν = 0.1 Hz) and at 373 K indicates that only these ions which have the large number of unpaired and unscreened electrons on the unfilled shells are responsible for the colossal dielectric effect.