Effect of rare earth yttrium substitution on the structural, dielectric and electrical properties of nanosized nickel aluminate

In this communication, we have systematically investigated the effect of yttrium substitution on the structural, dielectric and electrical properties of nanosized NiAl2−2xY2xO4 series (where x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.07 and 0.10). All the samples were prepared by chemical coprecipitation method. Powder X-ray diffraction (XRD) confirmed the formation of single phase cubic spinel structure in all the samples. Replacement of Al3+ ions by Y3+ ions results in a slight increase of lattice parameter. It was inferred that the substitution of yttrium suppressed the crystallite size growth. Transmission electron microscopy (TEM) validated the nanocrystalline nature of the samples. The Fourier transform infrared spectroscopy (FTIR) confirmed the preference of Y3+ ions at the octahedral B site. Room temperature dielectric properties, namely dielectric constant (ɛ′), dielectric loss (tan δ), ac conductivity (σa.c.) and electrical modulus (M″) were studied as a function of applied frequency in the range from 1 kHz to 1 MHz. These studies indicate that all the samples show usual dielectric dispersion which is due to Maxwell-Wagner type Interfacial Polarization. The ac conductivity measurement suggests that the conduction mechanism is due to small polaron hopping. The electrical modulus results clearly indicate the presence of non-Debye type of dielectric relaxation in all the samples. The dc electrical resistivity measured in the temperature range of 303-373 K was found to increase with temperature and yttrium content.