UC Berkeley

The field of material science and engineering aims to provide interdisciplinary communities with the physical understanding and control of various material structures and properties to allow for the development of advanced material systems and technology. Key to the developments of ubiquitous energy conversion, enhanced computer logic and memory performance, and artificial intelligence lies an increasing demand for highly-susceptible, next-generation materials which maintain unique functional ability under applied thermal, mechanical, and electrical stimuli. One such class of functional materials poised to address these needs are thin-film, complex-polar oxides which maintain a rich landscape of electromechanical, thermoelastic, and electrothermal properties. As such, although developments in the fields of dielectrics, piezoelectrics, and ferroelectrics have followed, the field of pyroelectrics (i.e., electrothermal response) has remained relatively understudied. Due to the complex material property intercoupling of pyroelectricity to dielectric, ferroelectric, and piezoelectric counterparts, identifying routes to understand and enhance the various contributions to pyroelectric response has continued to limit the field. As a result, pyroelectrics have remained primarily stagnant in the past 30 years, limited to applications only in IR sensor array technology. Without the proper understanding and control of the various material properties that contribute to the overall pyroelectric response needed for enhanced performance in next-generation applications (e.g., waste-heat energy conversion), researchers have traditionally defaulted to perching pyroelectric systems near material phase transitions. Specifically, proximity to the Curie transition temperature (T_C) typically allows for the overall enhancement of pyroelectric response, however, at the cost of small operating temperature windows and increased DC, background temperatures. In this Dissertation, I aim to elucidate the various contributions to pyroelectricity via comprehensive and direct characterization methodologies and provide the community with accessible routes for overall pyroelectric response enhancement . I aim to show that these coupled material properties do not simply follow design rules established in the fields of ferroelectric and piezoelectric materials, and thus require an unintuitive understanding of their interactions.In this work, I provide various insights into the complex pyroelectric property interplay in prototypical PbZrxTi1-xO3 and BaTiO3 thin-film ferroelectric oxides. With careful consideration of applied electric fields, temperature oscillations, and device geometry, I show that pyroelectric contributions may be individually suppressed and decoupled to provide quantitative understanding in overall pyroelectric response. With the engineering of domain architectures in PbZrxTi1-xO3 systems via underlying substrates, the evolution of ferroelectric, dielectric, and pyroelectric response is investigated to understand and quantify ferroelastic- domain contributions. Typically disregarded in the past, I demonstrate that these subtle extrinsic contributions may account for as much as 35% of the total measured pyroelectric response at room temperature for some films. Furthermore, through the use of applied, high-DC electric fields , I can systematically suppress these extrinsic contributions to understand the evolution of pyroelectric response across the morphotropic boundary of PbZrxTi1-xO3. Lastly, with the fabrication and synthesis of in-plane electrothermal test platforms and high-quality BaTiO3 thin-films on Si substrates, I systematically investigate the evolution of elastic boundary conditions on the extrinsic and secondary contributions to pyroelectricity. Through the quantification of the various pyroelectric contributions, I more clearly depict the underlying property complexities that have long hindered advancements in the field of pyroelectrics.