We report a non-Pb piezoelectric ceramic system $\mathrm{Ba}({\mathrm{Ti}}_{0.8}{\mathrm{Zr}}_{0.2}){\mathrm{O}}_3\mathrm{\text{−}}({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{TiO}}_3$ which shows a surprisingly high piezoelectric coefficient of $d_{33}\sim 620\mathrm{pC}/\mathrm{N}$ at optimal composition. Its phase diagram shows a morphortropic phase boundary (MPB) starting from a tricritical triple point of a cubic paraelectric phase ($C$), ferroelectric rhombohedral ($R$), and tetragonal ($T$) phases. The high piezoelectricity of the MPB compositions stems from the composition proximity of the MPB to the tricritical triple point, which leads to a nearly vanishing polarization anisotropy and thus facilitates polarization rotation between $⟨001⟩T$ and $⟨111⟩R$ states. We predict that the single-crystal form of the MPB composition of the present system may reach a giant $d_{33}=1500–2000\mathrm{pC}/\mathrm{N}$. Our work may provide a new recipe for designing highly piezoelectric materials (both Pb-free and Pb-containing) by searching MPBs starting from a TCP.

We report here “strain glass,” a new glassy phenomenon in ferroelastic-martensitic system of Ni-rich intermetallic ${\mathrm{Ti}}_{50-x}{\mathrm{Ni}}_{50+x}$ ($x>1$), where local strain is frozen in disordered configuration below a critical temperature $T_g$. The ac elastic modulus shows a minimum at $T_g$, which exhibits logarithmic frequency dependence following Vogel-Fulcher relationship, and the corresponding internal friction shows a frequency-dependent peak located at a lower temperature. In situ high-resolution transmission electron microscopy observations reveal uncorrelated nanoclusters of martensiticlike phase, randomly frozen in the otherwise untransformed parentlike matrix. Being parallel to spin glass and relaxor, strain glass may shed new light on the fundamental physics of glass and lead to the discovery of novel properties.