New complex materials with enhanced ability to convert mechanical stress into electrical energy and vice versa
The motivation – In the world of advanced functional materials for developing improved technological goods, so-called piezoelectric and ferroelectric materials are unique in their ability to generate electricity with the application of pressure and change shape upon application of a voltage. These remarkable properties make piezoelectrics and ferroelectrics an important class of functional materials for electromechanical sensing and actuating purposes. For example, thanks to their physical properties, piezoelectrics are used in medical ultrasonic devices for imaging, diagnosis and therapy, in machine tool controllers, in 3D printer heads, and in energy harvesters. They also have many other uses, including in devices for precision positioning and underwater detection and navigation (sonar). With such a wide variety of modern applications, it is not surprising that there is an increasing demand for more responsive piezoelectric materials for cutting-edge technologies.
The discovery – Many of the materials used in technological applications adopt what is known as a ‘complex perovskite structure’. A perovskite structure is a type of crystal structure that mimics the structure found in the naturally occurring mineral calcium titanium oxide. In this study, the Ye group at Simon Fraser University along with their research colleagues in China (including a visiting research student) used the crystal chemistry features of bismuth-based complex perovskites to design and synthesize a material that exists as a solid solution; they did this by alloying a complex perovskite compound [ Bi(Zn2/3Nb1/3)O3] with one of the most commonly used piezoelectric materials [Pb(Mg1/3Nb2/3)O3-PbTiO3]. These researchers prepared a series of new compounds, described by the generalized structure (0.95-x)Pb(Mg1/3Nb2/3)O3-0.05Bi(Zn2/3Nb1/3)O3-xPbTiO3, and then used various analytical techniques to characterize each new compound according to its properties (i.e., crystal structure, phase transformation behaviour, local polar structure, ferroelectric properties and piezoelectric response).
The outcome of their detailed characterization work is that these new materials have significantly enhanced properties when compared to the commonly used piezoelectric materials. Of particular interest to functional materials scientists, the piezoelectric coefficient of this new compound is 20% higher than that of the traditional piezoelectric ceramics (i.e., the coefficient of the new compound reaches 805 pC/N, whereas the traditional material has a coefficient of 669 pC/N). More interestingly, the incorporation of Bi(Zn2/3Nb1/3)O3 into Pb(Mg1/3Nb2/3)O3-PbTiO3 results in the suppression of the depoling behaviour of the traditional piezoelectric ceramics; as this depoling behaviour is an ongoing problem for the traditional piezoelectric material when it is at relatively low temperatures, the new materials offer great potential for expanding the functional operating temperature range of piezoelectrics.
Its significance – These improved properties make the new family of materials a promising candidate for applications in electromechanical sensors and actuators, high energy density capacitors, and other devices to be used in advanced technologies. Furthermore, the fundamental crystal chemistry concepts, successful synthetic method and complete characterization of the structures and physical properties described in this work can be applied to the development of other bismuth-related piezo-/ferroelectric materials of complex perovskite structure with higher performance in the future.
Read the paper – “Synthesis, structure and piezo-/ferroelectric properties of a novel bismuth-containing ternary complex perovskite solid solution” by Liu, ZH; Paterson, AR; Wu, H; Gao, P; Ren, W; Ye, ZG. Journal of Materials Chemistry C 5(6):3916–3923 (2017). DOI: 10.1039/C7TC00571G