The electronic and magnetic properties of LaCrO4 and Nd1-xCaxCrO4 (x=0-0.2) and the conduction mechanism

The electric conductivity of monazite-type LaCrO4 and zircon-type Nd1-xCaxC rO4 (x = 0-0.2) were characterized by measurements of dc electric conductiv ity and the Seebeck coefficient in the 300-600 K range. The LaCrO4 and NdCr O4 were found to be n-type semiconductors, while commonly known monazite- o r zircon-type oxides are insulators. In mixed valence compounds of Cr-V and Cr-VI, Nd1-xCaxCrO4 (x = 0.1, 0.2), hole hopping conduction arising from t he mixed valency was also observed. The Nd1-xCaxCrO4 (x = 0.1, 0.2) compoun ds obeyed Curie-Weiss behavior above the Neel temperature, and the observed magnetic moments for the Cr-V ions were in good agreement with the theoret ical values. Experimental results and the calculated spin densities by the UHF method indicated that most of the unpaired electrons from Cr-V were loc alized on Cr atoms. The ab initio MO calculations for CrO43- clusters in Nd CrO4 revealed that the SOMO is the degenerate d pi* state and that the LUMO is the p sigma* state (O 2p origin): the SOMO forms the degenerate states at the top of the valence band and the LUMO forms a wide conduction band. F or NdCrO4 and LaCrO4 the electronic conduction mechanism as semiconductors was explained by the band model. For Nd1-xCaxCrO4 (x = 0.1, 0.2) electronic conduction was described by the band model combined with hopping conductio n of holes in degenerate d pi* states. It is concluded that the electronic conductivity of these compounds is caused by an intermixing of the ligand-t o-metal charge-transfer (LMCT) state into the ionic configuration.