91 ISSN 1087-6596, Glass Physics and Chemistry, 2017, Vol. 43, No. 1, pp. 91–97. © Pleiades Publishing, Ltd., 2017. Effect of Sr Addition on Piezoelectric Properties and the Transition Temperature of BaTiO 3 1 A. Elbasset a, *, S. Sayouri b , F. Abdi a , T. Lamcharfi a, b , and L. Mrharrab b a Laboratory of Signals Systems and Components FST Street Immouzar, B. P. 2202 Fez, Morocco, b Laboratory of Physics, Theoretical and Applied, FSDM B. P. 179, Fez. Morocco *e-mail: elbasset.abdelhalim@gmail.com Received May 18, 2015 Abstract–Single phased Sr substituted BaTiO 3 ceramics were synthesized by a sol-gel route and were found to crystallise in tetragonal symmetry with P 4mm space group using rietveld refinement. With increase in Sr content the tetragonality was reduced to pseudocubic and the Curie temperature (T c ) decreased with a rate of 3.33 K/mol %. This transition temperature has been determined by studying the thermal evolution of Cole- Cole diagrams (ε'' vs ε'). Effects of Sr content (x) and sintering time (4 and 8 h) on density, crystalline struc- ture and piezoelectric properties were also investigated. Keywords: Cole–Cole plot (ε'' vs ε'), the transition temperature (T c ), planar coupling coefficient k p , piezo- electric constant d 33 DOI: 10.1134/S1087659617010059 INTRODUCTION Perovskites with general formula, ABX 3 , due to their excellent electric and magnetic properties, are extensively used for detectors, computer memories, pyroelectric detectors, multilayer ceramic capacitors, field devices, and sensors [1–7]. These materials have very flexible structure and a variety of cations can be substituted in their lattices to enhance their intrinsic properties. BaTiO 3 it is also considered as one of the alternatives to the Pb based materials that do not pre- serve environment. Various dopants like Sr 2+ , Ca 2+ ions at A site and/or Zr 4+ , Mn 4+ , Nb 5+ ions at B site are known to shift the phase transformation tempera- ture in BaTiO 3 making it suitable for high or low tem- perature piezoelectric devices [8]. Barium strontium titanate has been among the most promising candidate for to the above cited applications due to its high dielectric response and its tunability near the ferro- electric phase transition temperature. The transition temperature can be controlled by adjusting Sr compo- sition [9]. The determination of this temperature is based on the evolution of the dielectric constant as a function of temperature [10–14]. However, literature survey reveals that the relationship between variations in the imaginary part of the permittivity as function of the real part and the temperature of transition have not been reported so far. Therefore, in this work, the atten- tion has been focused on the evolution the Cole-Cole diagram (ε'' vs ε') depending on the temperature of measurement. In this aim we are also interested in the study of some piezoelectric coefficients and their dependencies with heat treatment time and dopant rates Sr. Moreover, the structures and densities of BaTiO 3 –xSr systems were also investigated. EXPERIMENTAL A series of Sr added BaTiO 3 (ВТ) ceramics (abbre- viated as BaTiO 3 –xSr, x = 0.0, 0.05, 0.10, 0.125 and 0.15, where x is mol % of Sr) were synthesized using the sol–gel method. For preparing the powders, we used as starting materials, barium acetate trihydrate, Ba(CH 3 COO) 2 · 3H 2 O (99% purity), titanium alcox- ide, Ti[OCH(CH 3 ) 2 ] 4 (97% purity) and strontium car- bonate, SrCO 3 (97.9% purity) without further purifi- cation. All chemicals were purchased from Johnson Matthey GmbH Alfa, Karlsruhe. The mixtures were dried and calcined at 1000°C for 4 h. The resultant powders were mixed with 2 wt % of polyvinyl alcohol and pressed into pellets of 12 mm in diameter and 1 mm in height by uniaxial pressing under a pressure of 10 tons/cm 2 . These pellets were surrounded by sacrifi- cial powder of the same composition and were sintered for 1 h at 600°C, this level was created for removing the PVA followed by a second level at 1100°C (for 8 or 4 h) reached with a heating rate 3 K/min. The density of the samples was determined by accurately measuring their mass, diameter and thickness. The formation of the crystalline phase of the sintered samples was ana- lyzed by X-ray diffractometry (XRD) at room tem- 1 The article is published in the original.