Impedance properties in magnetic-dielectric Zr0.8Cr0.2O2 Nanocrystallites

A compound Zr_0.8Cr_0.2O₂ upon adding Cr⁴⁺(3d2) spins in a dielectric host ZrO₂ exhibits impedance, magnetic and other functional properties. Small Zr_0.8Cr_0.2O₂ crystallites (5 nm average size) of a cubic ZrO₂-like phase are obtained by heating a polymer precursor at 425 K temperature in ~0.6 bar pressure in an autoclave and then at 775 K for 2 h in ambient air. The sample reflects the Curie point (TC) as a distinct peak/transition in the real (Z\´) and imaginary (Z") impedance. The TC shifts from 505 K to ~585 K with increasing the frequency from 0.1 kHz to 100.0 kHz. The Z\´-value traces a plateau below ~20.0 kHz and that widens progressively from 555 K to 615 K. The Z"-value exhibits a relaxation peak at ~8 kHz at 555 K and that shifts to higher frequencies with increasing temperature, reaching ~50 kHz at 615 K. The activation energy of relaxation of charge carriers drops from 1.76 eV over 550-580 K to 0.63 eV over 580-625 K in spin-disorder just above the TC.