W911NF-17-S-0002 Research Topic: International Research Interests: Innovations in Materials Si-compatible electrostrictive materials with low dielectric constant and low elastic compliance
Abstract
Materials undergoing large (=100 ppm) deformation under applied electric field, i.e., electrostrictors and piezoelectrics, constitute the backbone of a number of critically important technologies. For electrostrictors, electric field, ÀÀ, and strain, ÀÀ, have a quadratic relationship, ÀÀÀÀ = ÀÀÀÀÀÀ á ÀÀÀÀ 2 , where M is the electrostriction strain coefficient. Thus, electrostrictors convert electrical energy into mechanical energy; but (importantly) not ÀÀÀÀÀÀÀÀ ÀÀÀÀÀÀÀÀÀÀ , making electrostrictive transducers insensitive to the pressure wave they create. Electrostrictive ceramics currently in use have two major drawbacks: large dielectric constants (ÀÀ>10000), requiring large driving currents, and incompatibility with Si-microfabrication. Strong, classical (Newnham) electrostrictors have either large dielectric constants or large elastic compliance, S . However, during the last decade, there were reports on inorganic oxides (doped CeO2 and (Nb,Y)-stabilized À-Bi2O3), which combine large M, small S and small ÀÀ, exceeding deformation values expected from classical electrostrictors by >100-fold. This Ònon-classicalÓ behavior has been attributed to electric field-induced reorientation of highly polarizable elastic dipoles resulting from aliovalent doping. In such a host-guest system, elastic and dielectric properties are defined by the host lattice, while electrostriction is defined by the polarizability and local strain of elastic dipoles. Three macroscopic properties- electrostriction strain coefficient, saturation strain and relaxation frequency - are a direct reflection of the microscopic properties of polarizable, elastic dipoles: local strain tensor, elastic dipole moment, polarizability, and orientational factor (asymmetry). Despite extensive literature (EXAFS, in particular) data on the local structure of undoped and doped ceria, it is yet not possible to relate dopant-induced local distortion to properties of a polarizable elastic dipole. The proposed research has two main objectives. I. Understanding the correlation between the electrostrictive properties of aliovalent-doped ceria ceramics and their composition. This includes determining: (a) the degree to which electrostrictive properties can be independently adjusted; and (b) their influence on intrinsic material parameters, such as the elastic modulus and dielectric constant. II. Achieving the first objective will lay the groundwork for demonstrating the feasibility (i.e. proof of concept) of ceria-based electrostrictive materials, combining: low dielectric constant (<200); weak elastic compliance (=5á10-12 Pa-1); longitudinal electrostriction strain coefficient >10-17 m2/V2 at f >100Hz; full compatibility with Si-microfabrication. The working hypothesis is that the amplitude of electrostrictive strain is determined by the concentration, mutual interaction, and strength of the polarizable elastic dipoles, whereas the relaxation time is determined by their ability to reorient (lability). The research will comprise preparation and characterization of doped ceria ceramics. It will include three (each ~ 12 months) stages: 1) investigation of doping with single , aliovalent cations, leading to construction of a multidimensional map correlating the three properties of the dopant (valence, size and concentration) with the three major macroscopic characteristics of electrostrictive strain (magnitude, saturation strain and relaxation frequency); 2) understanding the effects of a single isovalent dopant and aliovalent/isovalent co-doping. By the end of this stage, a model linking the properties of the elastic dipoles with our electrostriction data, as well as with our (published) EXAFS data, will be constructed; 3) optimization of composition based on this model and testing of the long-term stability of the electrostriction properties.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF2110263
Entities
People
- Igor Lubomirsky
Organizations
- Army Contracting Command
- United States Army
- Weizmann Institute of Science