Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Comparative structural and optical studies on pellet and powder samples of BaTiO 3 near phase transition temperature Vikash Mishra a , Anil Kumar b , Archana Sagdeo c,d , P.R. Sagdeo b,* a Department of Physics, Indian Institute of Technology Bombay, Powai Mumbai, 400076, India b Material Research Laboratory, Discipline of Physics and MEMS, Indian Institute of Technology Indore, Indore, 453552, India c Indus Synchrotron Utilization Division, Raja Ramanna Center for Advanced Technology Indore, 452013, India d Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, 400094, India ARTICLE INFO Keywords: Barium titanate Phase transition Optical properties Structural properties Strain ABSTRACT In order to investigate the possible effect of inter-granular strain on the physical properties of Barium titanate (BaTiO 3 ), comparative studies have been carried out on the polycrystalline pellet and its corresponding powder samples. For this purpose, the polycrystalline pellet sample of BaTiO 3 has been prepared via conventional solid- state reaction route and powder is obtained by crushing the part of the prepared BaTiO 3 pellet. The comparative room temperature structural studies, temperature dependent optical and Raman spectroscopy measurements have been carried out on the prepared pellet and powder samples. Room temperature X-ray diffraction and Raman analysis confirms the presence of extra amount of strain in pellet sample compared with that of the powder sample. Temperature dependent Raman analysis also suggests the difference in the high temperature tetragonal to cubic transition temperature in both cases. Temperature dependent optical absorption properties measured in terms of Urbach energy (E U ), Urbach focus (E 0 ) and Urbach relaxation clearly indicates the sig- nificant change in these quantities for both types of samples on BaTiO 3 . Present results strongly reveal the difference in structural, optical and vibrational properties of BaTiO 3 especially across phase transition in pellet and its corresponding powder which clearly shows the importance of inter-granular strain at the grain bound- aries. 1. Introduction In the case of ferroelectric material, it is well known that strain plays very crucial role [1–4]. Recently, strain engineering has been used experimentally to stretch the electric polarization in BaTiO 3 and PbTiO 3 up to 400μC/Cm 2 which enhances the corrosivity [1–3]. In the case of similar ABO 3 type of perovskites i.e. Ca-doped LaMnO 3 , Sagdeo et al. [5,6] reported that the interfacial strain present near grain boundary is responsible for the structural phase coexistence observed in these types of materials. Thus, it appears that the perovskite-based oxides, which undergo the structural phase transition [4,7] as a function of tem- perature or pressure, the interfacial strain can play a very crucial role. Barium titanate which is being investigated by various researchers for ferroelectric properties is known for various structural phase transitions [8–13]. Recently Anil Kumar et al. have shown that the optical prop- erties are very sensitive to the strain [14]. Our recent temperature dependent optical investigations on the polycrystalline pellet samples on BaTiO 3 15 clearly demonstrates that across the phase transition there exist relaxation behavior in Urbach energy (E U )[16,17]. It is now well established that the polycrystalline strained pellet and the corre- sponding almost strain free polycrystalline powder samples show dif- ferent behavior as a function of temperature [5,6]. Further physicists and material scientists perform most of the experiments on the poly- crystalline solid pellet samples whereas for the first principle in- vestigations the structural data (x-ray or neutron diffraction) collected on the polycrystalline powder sample is generally used to predict the electronic structure and other physical properties. In fact, in our earlier publication [15] on the optical and electronic properties of BaTiO 3 we have done the structural characterization on powder samples whereas the optical properties have been investigated on polycrystalline pellet sample. Keeping this in view, in the present studies the comparative optical absorption spectroscopy [16–19] on the pellet and the corresponding powder samples of BaTiO 3 has been carried out. Interestingly, it has been observed that the value of E U shows more relaxation in pellet sample compared to that of powder samples. The results may be https://doi.org/10.1016/j.ceramint.2019.10.030 Received 16 August 2019; Received in revised form 26 September 2019; Accepted 4 October 2019 * Corresponding author. E-mail address: prs@iiti.ac.in (P.R. Sagdeo). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Vikash Mishra, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.10.030