Piezoelectricity in Nominally Centrosymmetric Phases

TL;DR

This study reveals that nominally centrosymmetric materials exhibit measurable piezoelectricity due to symmetry-breaking effects, detected through highly sensitive Resonant Piezoelectric Spectroscopy, challenging traditional notions of symmetry constraints.

Contribution

It demonstrates the ubiquity of symmetry-breaking piezoelectricity in nominally centrosymmetric and disordered materials using advanced spectroscopy techniques.

Findings

Piezoelectricity observed in all nominally cubic phases.

Effective piezoelectric coefficients range from 1 pm/V to 10^-5 pm/V.

RPS is highly sensitive, detecting coefficients below conventional measurement limits.

Abstract

Compound phases often display properties that are symmetry-forbidden relative to their nominal, average crystallographic symmetry, even if extrinsic reasons (defects, strain, imperfections) are not apparent. Here, we investigate macroscopic inversion symmetry breaking in nominally centrosymmetric materials and measure Resonant Piezoelectric Spectroscopy (RPS) and Resonant Ultrasound Spectroscopy (RUS) in 15 compounds, 18 samples, and 21 different phases, including unpoled ferroelectrics, paraelectrics, relaxors, ferroelastics, incipient ferroelectrics, and isotropic materials with low defect concentrations, i.e. NaCl,cfused silica, and CaF2. We exclude the flexoelectric effect as a source of the observed piezoelectricity yetcobserve piezoelectricity in all nominally cubic phases of these samples. By scaling the RPS intensities with those of RUS, we calibrate the effective piezoelectric coefficients using single crystal quartz as standard. Using this scaling we determine the effective piezoelectric modulus in nominally non-piezoelectric phases, finding that the "symmetry-forbidden" piezoelectric effect ranges from 1 pm/V to 10E-5 pm/V. The values for unpoled ferroelectric phases are only slightly higher than those in the paraelectric phase of the same material. The lowest coefficients are well below the detection limit of conventional piezoelectric measurements and demonstrate RPS as an ultra-highly sensitive method to measure piezoelectricity. We suggestt hat symmetry-breaking piezoelectricity in nominally centrosymmetric materials and disordered, unpoled ferroelectrics is ubiquitous.