Giant Strains in Non-Textured (Bi1/2Na1/2)TiO3-Based Lead-Free Ceramics

Abstract

<p><strong></strong>Recent intense research on lead-free piezoceramics has led to the discovery of many oxide ceramics with excellent properties.[<a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201503768/full#adma201503768-bib-0001" title="Link to bibliographic citations">1-4</a>] Among reported solid solution families, the bismuth-alkali titanate-based system develops the largest strain under applied electric field (0.45%–0.48%),[<a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201503768/full#adma201503768-bib-0005" title="Link to bibliographic citations">5-7</a>] making it a promising material for applications in actuators.[<a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201503768/full#adma201503768-bib-0008" title="Link to bibliographic citations">8, 9</a>] However, high electric fields are required in this system, resulting in a low <em>d</em>₃₃* (the large-signal piezoelectric coefficient). Values of <em>d</em>₃₃* greater than 1000 pm V⁻¹ were reported in barium titanate- and alkali-niobate-based families, but the achievable electrostrain is quite low (often below 0.3%).[<a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201503768/full#adma201503768-bib-0010" title="Link to bibliographic citations">10-12</a>] Single crystals possess remarkable values for both <em>d</em>₃₃* and electrostrain,[<a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201503768/full#adma201503768-bib-0013" title="Link to bibliographic citations">13, 14</a>] the difficulties in fabrication and associated high cost have yet to be overcome for production in quantity. In this Communication, we report giant electrostrain (0.70%) and <em>d</em>₃₃* (1400 pm V⁻¹) in a non-textured lead-free polycrystalline ceramic. These excellent properties are attributed to electric-field-induced phase transitions, according to in situ transmission electron microscopy (TEM) examinations. The results are directly beneficial to next-generation actuators, and may also shed light on the development of deformable structural ceramics.</p>