Understanding the impact of Ca doping on structural, morphological and low temperature transport properties of Nd2NiMnO6

Abstract

Double perovskites of the form R2NiMnO6 (R=Rare-earth) are recognized for their multifunctional nature. Here in this study we have considered one of the members of this class of double perovskites i.e., Nd2NiMnO6 and modified its various physical properties through Ca doping at Nd site. X-ray diffraction patterns and their analysis show the monoclinic structure that can be indexed with P21/n space group for all the three compounds of Nd2-xCaxNiMnO6 (x = 0.0, 0.2 and 0.4). Scanning electron microscopy shows that the grains are irregular in shape and size for the three samples and the average grain size decreases with increase in Ca concentration. The variation of dielectric constant as well as dielectric loss with frequency depicts a decrease in their value with increase in frequency from 20 Hz to 2 MHz. On the other hand the variation of dielectric constant with temperature shows a rise in the value of dielectric constant as the temperature is increased from 100 K to 300 K, while the temperature variation of dielectric loss is associated with relaxation behavior. The peak in the tanδ curve corresponds to the temperature at which the dielectric constant starts increasing and this peak in the dielectric loss gets shifted towards the side of high temperature with the rise in frequency. A rise in the Ca concentration increases the dielectric constant as well as dielectric loss. The ac conductivity for all the three samples of Nd2-xCaxNiMnO6 (x = 0.0, 0.2 and 0.4) rises with rise in temperature indicating the existence of negative temperature coefficient of resistance. The ac conductivity also increases with increase in Ca concentration. A further analysis of conductivity behavior has been done by determining the activation energy through the involvement of the Arrhenius equation. The activation energy decreases with increase in Ca concentration. The resistivity measurements again indicate the existence of negative temperature coefficient of resistance in all the three samples of Nd2-xCaxNiMnO6 (x = 0.0, 0.2 and 0.4) and the value of resistivity reduces as the Ca concentration is increased. The various results obtained in this study have been interrelated.