Dipole relaxation process and giant dielectric permittivity in Eu3+- doped CdMoO4 single crystal

Abstract

Single crystal of Eu3+-doped cadmium molybdate (Cd0.9268 M 0.0244Eu0.0488MoO4, where M denotes cationic vacancies) has been successfully grown by the Czochralski method in air and under 1 MPa. X-ray diffraction analysis indicates that as-grown single crystal exhibits tetragonal scheelite-type structure (a = b = 5.16188(14) A; c = 11.2080(5) A; space group I41/a). Eu3+ ions do not show long-range order and they are randomly distributed in CdMoO4 framework substituting Cd2+ ones. UVevis diffuse reflectance measurements revealed very close optical band gap (Eg) values, i.e. ~1.74 eV along [100] and [001] crystallographic directions that are twice smaller than Eg of microcrystalline pure CdMoO4 as well as powder Eu3+-doped single crystal. Magnetic and electrical studies of Eu3+-doped cadmium molybdate single crystal showed a paramagnetic and n-type semiconducting behaviour with the metal-insulator transition above 350 K along both crystallographic directions. Dielectric results analysis using the Cole-Cole fit function revealed that the dipole relaxation process has different time scale depending on the crystallographic direction and exhibits Arrhenius temperature dependence for both studied directions. This fact is accompanied by the colossal dielectric permittivity with er > 8 • 103. The above results are considered in the framework of narrow europium multiplets of energy comparable to thermal energy.