The discovery of ferroelectricity in BaTiO₃₀ [1] , fascinated the young researchers and scientists into the field of materials research. As a result, a large number of oxides of different structures such as perovskite, tungsten bronze, layer structure etc., have been studied for their applications in devices like transducers, actuators, multi-layer capacitors, ferroelectric random access memory and display, microwave dielectric resonators etc. [2] - [7] . This activated the researchers to develop and design thermally stable new electronic materials possessing high dielectric constant and low dielectric loss. In this context, some ferroelectric oxides of tungsten bronze (TB) structural family have been widely investigated because their favorable dielectric properties show wide applications in devices. The TB structure consists of a complex array of distorted BO₆ octahedral sharing corners in such a way that three different types of interstices (A, B and C) are available for cation substitutions in a general formula (A₁)₂(A₂)₄(C)₄ (B₁)₂(B₂)₈O₃₀. Mono or divalent cations can be accommodated at A₁ and A₂ sites, tri or pentavalent cations at octahedral sites B₁ and B₂ [8] , with C site (smallest interstice) generally empty; hence the general formula for tungsten bronze structure is A₆B₁₀O₃₀. It is an observed fact that the substitution of varieties of cations at the A and B sites (with different size and charge distribution) causes a significant variation in the physical properties of the materials [9] . Further, since the structural and/or micro-structural changes in a system drastically modify their physical properties, a detailed study of electrical (impedance) properties of Sr-substituted Ba₅GdTi₃V₇O₃₀ (BSGTV) assumes greater significance in order to have a complete picture of properties of these ceramics. This aspect has motivated us for the present work comprising of a detailed analysis of the effect of dopant concentration on electrical properties of Sr-modified BGTV.

The series of ceramic compound Ba_5-xSr_xGdTi₃V₇O₃₀ (BSGTV) (x = 0 - 5) have been synthesized with Sr substitution by mixed oxide process. High purity (AR grade) oxides and carbonates, BaCO₃, SrCO₃, Gd₂O₃, TiO₂, V₂O₅ (M/S Sarabhai M. Chemicals, India) in a suitable stoichiometry were weighed, thoroughly mixed and then grounded in dry (air) and wet (methanol) medium for 2 h each in an agate mortar. Calcination of the grounded mixtures was done at an optimized temperature and time (950˚C for 24 hs). Pellets were prepared from the calcined powder with addition of a small amount of polyvinyl alcohol by applying a uniaxial pressure of 5 × 10⁶ N/m². The pellets were subsequently sintered at an optimized temperature 10,000˚C for 12 hs. in an air atmosphere using high purity alumina crucibles. The formation and quality of the compounds were checked using X-ray diffraction (XRD) technique. The X-ray diffraction patterns of the compounds were recorded at room temperature using an X-ray powder diffractometer (Rigaku, Miniflex) with CuK_α radiation (1.5405 Ǻ) in a wide range of Bragg’s angles 2θ (20˚ ≤ 2θ ≤ 80˚) with a scanning rate of 30/min. The XRD peaks of all the samples are observed to be different from that of the ingredients, suggesting the formation of new single phase compounds. All the peaks were indexed taking their 2θ values using a computer program package, “POWDMULT” [10] in different crystal system and cell configuration. On the basis of the best agreement (based on least-squares refinement) between observed (obs) and calculated (cal) interplaner distance d (i.e., Σ(d_obs − d_cal) = minimum), an orthorhombic unit cell was selected. The Structural properties of compounds are reported earlier [11] . Surface morphology of the sintered pellets was studied at room temperature using scanning electron microscope (SEM) (JEOL-JSM-5800). The samples were preheated to 1500˚C for 4 hs to remove the moisture, if any. Measurements of impedance, electrical modulus and conductivity as a function of temperature (30˚C - 500˚C) at different frequency (1 kHz - 1 MHz) were carried out using computer interfaced impedance analyzer PSM 1735, model: N4L. Silver electrodes were deposited on the polished surfaces of pellets to perform the above studies.

An analysis of the electrical properties of Sr-modified Ba₅GdTi₃V₇O₃₀ is reported in this paper using an AC impedance technique. Conventional Mixed Oxide process was used to synthesize the compound which was confirmed by X-ray diffraction studies. Appearance of two merged semicircular arcs at high temperatures (≥300˚C) for Sr modified BGTV compounds observed in the complex planes, interprets that the electrical response of the compounds is due to the grain and grain boundary effect, whereas, the presence of temperature dependent single semicircular arcs for pure BGTV compound shows that the electrical response is due to grain only. It has been observed that Sr substitution at the Ba-site has enhanced the barrier properties of the material, which results in a corresponding decrease in the electrical conduction. This may be due to the weakening in the capacitive (reactive) effects resulting in an enhancement of the bulk resistance on Sr substitution. Modulus analysis indicated the presence of non-Debye type conductivity relaxation in the materials.

Mohanty, B.B., Sahoo, P.S., Giri, B.K., Panda, J.N. and Choudhary, R.N.P. (2018) Effect of Strontium Substitution on Impedance Properties of Ba₅GdTi₃V₇O₃₀ Ceramics. Journal of Modern Physics, 9, 620-627. https://doi.org/10.4236/jmp.2018.94043