Enhanced dielectric and piezoelectric properties of Ba₀.₈Sr₀.₂Ti₁-𝑥Sn𝑥O₃ for energy harvester applications

Piezoelectricity improved our daily life by producing many useful applications such as automotive fuel injection, accelerometers, piezoelectric transformers and motors, vibration control, micro-positioning systems, ultrasonic sensor, generators, inkjet printers, and energy harvester. The energy harvester is used to convert force into electrical energy. Piezoelectric material becomes the most attention than other material because the material itself can directly convert applied strain energy into electrical energy. However, the most practical piezoelectric material available in the market is Lead Zirconate Titanate (PZT) which contained a large amount of Lead (Pb) that gives severe implications to the environment. This situation has forced the finding of lead-free piezoelectric material in recent years. Barium Titanate (BaTiO₃)-based ceramic has become the promising candidate that could have comparable properties to Pb when doped with other elements. In this study, Ba₀.₈Sr₀.₂Ti₁-𝑥Sn𝑥O₃ where x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 were prepared using conventional solid-state reaction method. The samples were characterised using X-ray Diffraction (XRD), Impedance Spectroscopy analyser, Piezoelectric Test analyser, and Scanning Electron Microscopy (SEM). The XRD analysis shows that Ba₀.₈Sr₀.₂Ti₁-𝑥Sn𝑥O₃ had a structural phase transition from tetragonal to cubic when Sn content increased. The dielectric analysis of, Ba₀.₈Sr₀.₂Ti₁-𝑥Sn𝑥O₃ shows the Curie temperature, Tc shifted towards lower temperature from 65 °C to 5 °C was due to the replacement of Sn4+ with larger ionic radii than Ti4+ at B-sites. The composition with x = 0 has the highest dielectric constant because of large spontaneous dipole moments. However, the substitution of Sn with x = 0.02 shows a bit decrease in dielectric constant. For x = 0.04, the dielectric constant has revealed two-phase transition at 40 °C (tetragonal – cubic phases) and another phase near ~ 25 °C, which belongs to orthorhombic – tetragonal phases (TO-T). The existence of orthorhombic – tetragonal phases (TO-T) has increased the dielectric constant. At x = 0.06 and 0.08, the dielectric constant decreases by increasing the Sn contents due to the structural changes to the cubic structure. However, the dielectric constant of the sample with x = 0.10 drastically increased due to the pinching effect where rhombohedral – orthorhombic (TR-O) phases and orthorhombic – tetragonal (TO-T) phases merged, forming one broad peak at Tc. The piezoelectric measurement shows that a sample with a tetragonal structure, x = 0, has a high d33 value about 95 pC/N, g33 value about 8.66x10-3 Vm/N has the high output power, P about 0.8227 pm3/J at room temperature, which is good for piezoelectric energy harvester application. When, Sn is doped in Ba0.8Sr0.2TiO3, the highest value of the piezoelectric constant d33 is 61 pC/N, the value of g33 is 3.77x10-3 Vm/N and has a high output power, P of 0.2300 pm3/J is recorded at x = 0.02.