Synthesis and Characterizations of Ferroelectric, Non-ferroelectric High Dielectric Constant Ceramics Modified BaTiO3 Systems for Multifunctional Applications

Abstract

High dielectric constant materials have become increasingly important due to their wide applications in the electronic industry as capacitors, sensors, actuators, power transmission devices, memory devices, high energy storage devices, etc. High dielectric constant is found both in the ferroelectric as well as in non-ferroelectric class of materials. For the present work, BaTiO3 is selected as the ferroelectric material. But, for dielectric applications, BaTiO3 has following disadvantages: (i) the maximum value of dielectric constant exist near Curie temperature; (ii) Curie temperature (~130 °C) is far away from the room temperature, (iii) temperature sensitive dielectric properties with sharp phase transition. These disadvantages hinder use of this material for various device applications at room temperature. Temperature stability of the dielectric properties of the BaTiO3 system can be enhanced by preparing its solid solutions with other compounds having temperature independent dielectric properties. High dielectric response has also been observed in relaxor ferroelectric like Pb(Mg1/3Nb2/3)O3. PbO based complex perovskite relaxor ferroelectric materials have some advantages over BaTiO3-based system like broad dielectric maxima and high dielectric constant (~30,000). Also, Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O are some of the non-ferroelectric systems with giant dielectric constant (~104-105) at RT and independent of frequency and temperature over a wide range. The selected series of BaTiO3 based materials synthesized by solid state reaction method are: 1. (1-x) BaTiO3-x Ba(Fe1/2Nb1/2)O3 (x=0, 0.02, 0.04, 0.06 and 0.08) 2. (1-x) BaTiO3-x CaCu3Ti4O12 (x=0, 0.02, 0.04, 0.06 and 0.08) 3. (1-x) BaTiO3-x Li0.30Cr0.02Ni0.68O (x=0, 0.02, 0.04, 0.06 and 0.08) 4. (1-x) BaTiO3-x Pb(Mg1/3Nb2/3)O3 (x=0, 0.02, 0.04, 0.06 and 0.08) Based on the highest dielectric properties along with parents system, the following best composition are synthesized by sol-gel route: 1. BaTiO3 2. Ba(Fe1/2Nb1/2)O3 3. 0.94 BaTiO3-0.06 Ba(Fe1/2Nb1/2)O3 Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O modified BaTiO3 ceramics were synthesized by solid state reaction route. XRD study confirmed single phase without any secondary phase peaks in Ba(Fe1/2Nb1/2)O3 and Li0.30Cr0.02Ni0.68O modified BaTiO3 ceramics. However, minor secondary CuO peaks along with major BaTiO3 peaks were observed for CaCu3Ti4O12 modified BaTiO3 ceramics. Experimental density increased for Ba(Fe1/2Nb1/2)O3 modified BaTiO3 ceramics compared to parent BaTiO3 ceramics with highest density obtained for x=0.06 composition of Ba(Fe1/2Nb1/2)O3 modified BaTiO3 ceramics. However experimental density decreased for CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O modified BaTiO3 ceramics. Average grain size was found to decrease for all the modified ceramics. RT highest dielectric constant (at 10 kHz frequency) ~4124, 1404 and 1844 were obtained in x=0.06, x=0.04 and x=0.06 composition of Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O ceramics. However, highest value of dielectric constant at Tc (at 10 kHz frequency) ~11353, 4113 and 7543 was obtained in x=0.04, x=0.02 and x=0.06 composition of Ba(Fe1/2Nb1/2)O3, CaCu3Ti4O12 and Li0.30Cr0.02Ni0.68O ceramics. The transition temperature was found to decrease for Ba(Fe1/2Nb1/2)O3 and Li0.30Cr0.02Ni0.68O modified ceramics however increased for CaCu3Ti4O12 modified ceramics. Diffusivity increased with modification in all the modified BaTiO3 ceramics. Saturated P-E loop was only obtained in x=0.02 composition of Ba(Fe1/2Nb1/2)O3 modified ceramics which turned into lossy loops with high leakage current density with further increase in Ba(Fe1/2Nb1/2)O3 content. Saturated P-E loops were obtained in x=0.02 to x=0.06 compositions and lossy loop in x=0.08 composition for CaCu3Ti4O12 modified ceramics. However, lowest value of remnant polarization and coercive field were obtained in x=0.04 composition with lowest value of leakage current density. Pinched hysteresis loops with low leakage current density were obtained in all the Li0.30Cr0.02Ni0.68O modified ceramics. However, lowest value of remnant polarization and coercive field were obtained in x=0.06 composition with lowest value of leakage current density. Pb(Mg1/3Nb2/3)O3 modified BaTiO3 ceramics were synthesized by solid state reaction route, by mixing calcination powder of BaTiO3 and Pb(Mg1/3Nb2/3)O3 system and sintered at optimized sintering temperature of BaTiO3 ceramics. Single phase peaks were obtained in XRD study without any secondary phase peaks. Experimental density increased for Pb(Mg1/3Nb2/3)O3 modified BaTiO3 ceramics compared to parent BaTiO3 ceramics with highest density obtained in x=0.06 composition. Microstructure confirmed bimodal distribution of grains, larger grains corresponding to BaTiO3 and smaller grains corresponding to Pb(Mg1/3Nb2/3)O3 phase. Highest value of dielectric constant at room temperature (at 10 kHz frequency) ~3447 was obtained in x=0.06 composition. From temperature dependent dielectric study, two transition peaks were observed. Ferroelectric phase transition was found to increase in x=0.02 composition and then decreased for x=0.04 to x=0.08 compositions. Diffusivity was found to increase with Pb(Mg1/3Nb2/3)O3 modification. Saturated P-E loops were obtained in Pb(Mg1/3Nb2/3)O3 modified ceramics. Remnant polarization and coercive field values along with leakage current density were found to decrease for x=0.02 to x=0.06 compositions and increased for x=0.08 composition. Selected composition 0.94BaTiO3-0.06Ba(Fe1/2Nb1/2)O3 along with the parent BaTiO3 and Ba(Fe1/2Nb1/2)O3 systems were synthesized by sol-gel route. 0.94BaTiO3-0.06Ba(Fe1/2Nb1/2)O3 was prepared by two different methods. In one method, all the precursors are taken from the starting itself, and the product obtained is abbreviated as BFN-A. In the second method, calcined powders of BaTiO3 and Ba(Fe1/2Nb1/2)O3 were mixed and then sintered; the product obtained is abbreviated as BFN-B. For modified ceramics, single BaTiO3 phase peaks were obtained in BFN-B system in comparison to BFN-A system where minor secondary phase peaks were also obtained as confirmed from XRD study. Experimental density was found to be higher in BFN-B system in comparison to BFN-A system. Finer grains with homogeneous distribution were obtained in BFN-B system, whereas inhomogeneous distributions of grains were observed in BFN-A system. High value of dielectric constant at room temperature and at 10 kHz frequency was obtained in BFN-B (~1618) system in comparison to BFN-A (~234) system. Dielectric loss was found to be high in both the ceramics, however comparatively lower in BFN-B system. The transition temperature was found to decrease with the BFN modifications along with diffused phase transition. Remnant polarization and coercive field were found to be high for modified system.