Engineering of Electromechanical Oxides by Symmetry Breaking

Abstract

Complex oxides exhibit a wide range of fascinating functionalities, such as ferroelectricity, piezoelectricity, and pyroelectricity, which are indispensable for cutting‐edge electronics, energy, and information technologies. The intriguing physical properties of these complex oxides arise from the complex interplay between lattice, orbital, charge, and spin degrees of freedom. Here, it is reviewed how electromechanical properties can be achieved/improved by artificially breaking the symmetry of centrosymmetric oxides via engineering thermodynamic variables such as stress, strain, electric field, and chemical potentials. The mechanisms that have been utilized to break the inherent symmetry of conventional materials that lead to novel functionalities and applications are explored. It is highlighted that access to “hidden phases,” which otherwise are prohibited, could uncover opportunities to host exotic properties, such as piezoelectricity, pyroelectricity, etc. This review not only reports how to engineer intrinsically nonpolar and centrosymmetric oxides for emergent properties, but also has implications for manipulating polar functional materials for better performance.

Non-classical electrostriction in calcium-doped cerium oxide ceramics

“…It was apparent that bulk ceria ceramics with these trivalent dopants, as well as undoped ceria, follow a non-ideal Debye-type frequency-dependent electrostriction relaxation in the intermediate/high-frequency regime (≥1–10 Hz). 7,10 Similar relaxation behaviour was also observed in epitaxial and heterostructure thin film configurations. 47,58 Such an effect is not observed in the CDC ceramics in this experiment, and it is anticipated that the electrostriction relaxation is possibly shifted towards much lower frequencies.…”

“…[1][2][3] In conjunction with these classical applications, recently, a "non-classical giant electrostrictive" property has been described in both bulk and thin lms of highly defective cerium oxide derivatives at room temperature. [4][5][6][7] This nding has opened up promising application perspectives in next-generation actuators as a potential replacement for lead-based Pb(Ti 1−x Zr x )O 3 (PZT) compounds widely utilized in the electromechanical industry.…”

“…10,16 Furthermore, unlike piezoceramics, grain size, grain boundaries, and other pinning effects have little modulation in altering the electrostriction response. 7,25 Other reports also indicate that electrodes can signicantly affect the electrostriction response due to electrochemical effects at the electrode/material interface. 10 Electrochemical reactions in doped ceria are not expected at low temperatures as ionic mobility and activation energies are high.…”

Enhanced Mechanical and Electromechanical Properties of Compositionally Complex Zirconia Zr1–x(Gd1/5Pr1/5Nd1/5Sm1/5Y1/5)xO2−δ Ceramics

“…The strain saturation and relaxation behaviors are distinctive for the 5−20 mol % RE 2 O 3doped ceria ceramics with cubic fluorite lattice symmetry, as shown in our previous reports. 22,25,36 From the slope of the strain vs E 2 plot in Figure 4a,b, the electrostrictive strain coefficient (M 33 ) was assessed and plotted as a function of electric field frequency in Figure 4c. As shown, the M 33 value is slightly higher in the CCZ-10 sample.…”

“…They hold properties like high ionic conductivity (0.01 S/cm at 600 °C), low thermal conductivity (1.5 Wm –1 K –1 at 1000 °C), high-temperature phase stability, high hardness (12.4 GPa), and fracture toughness (10 MPa*m 1/2 ) . Moreover, unconventional mechanical (room temperature creep) and electromechanical characteristics have been observed in oxygen-defective fluorites, such as newly advanced CeO 2−δ and δ-phase-Bi 2 O 3‑δ . − These properties were associated with the presence of charge-compensating oxygen vacancies in the fluorites, whch are mostly dopant-controlled. , In many HEO systems, high-entropy fluorite-structured oxides (HEFOs) have drawn much attention for their compositional design and modified performance . Gild et al fabricated a series of bulk single-phase high-entropy fluorite oxides HEFOs, e.g., (Zr 0.2 Ce 0.2 Hf 0.2 )­(Y 0.2 Gd 0.2 )­O 2 , with equimolar ZrO 2 –CeO 2 –HfO 2 as the matrix with lower thermal and electrical conductivity than YSZ .…”