Structure of EuCrO4 and its electronic and magnetic properties

Single phase zircon type EuCrO4 (S.G. I4(1)/amd) was synthesized and the structure including atomic positions was precisely determined by X-ray Rietveld refinement. The electronic and magnetic properties of the compound were studied based on the electric conductivity, Seebeck coefficient, Raman spectroscopy, Mossbauer spectroscopy, magnetic susceptibility, and specific heat. The CrO43- tetrahedra in EuCrO4 were slightly elongated compared with that in NdCrO4, which caused splitting of the degenerated vibration modes of CrO43-, nu(2) and nu(3), in the Raman spectra. The Eu-151 Mossbauer spectra showed not a trace of the Eu(II) species in the compounds measured in the present work. The Debye temperature, Theta(D), estimated from Mossbauer spectra suggested that the vibrational state of Eu(III) in EuCrO4 was similar to that in the perovskite-type EuCrO3. However, the isomer shift of Mossbauer spectra revealed that the electron density of the 6s orbital of Eu(III) in EuCrO4 was very low and almost the same as that in the zircon type EuVO4, that is, Eu(III) in these compounds has highly ionic character, whereas the electron density of the 6s orbital of Eu(III) in EuCrO3 was higher and nearly the same as that in Eu2O3. EuCrO4 was found to be an n-type semiconductor similar to NdCrO4, while zircon type REMO4 (RE: rare earth metal(III); M: V, P, As, etc.) are insulators. Magnetic susceptibility and specific heat measurements showed that antiferromagnetic transitions took place at around 15 K and was solely due to Cr(V) from the magnetic entropy value of 5.54 J mol(-1) K-1.