The trouble with lead is that it is so useful. Although the least revered of the classical mretals, its physical, chemical and mechanical properties gave it virtues that the ancients appreciated. Malleability, low melting point and relative inertness recommended it for plumbing, stained-glass-window casements, solder and roofing; the strongly coloured compounds provided artists' pigments until the nineteenth century. That was when lead's toxicity became most pressing, not least because of industrial-scale manufacture of lead white paint. The recent scare over lead paints on cheap toys from China shows that this issue is still present, while lead-acid vehicle batteries now leak the poisonous heavy metal into landfills worldwide.

The drive to eliminate lead from commercial materials is also proceeding in more sophisticated applications, notably piezoelectrics. Lead zirconate titanate (PZT) has for several decades been the canonical piezoelectric material, which interconverts electrical and mechanical energy. PZT is the exemplary smart material, used in all manner of sensors, actuators and transducers from vibration dampers to sonar equipment. But the presence of lead is a drawback not only for environmental reasons. It also confers a relatively high density — a hindrance in some applications, for example because it produces a high acoustic impedance. And PZT does not work at high temperatures.

That's why alternative lead-free piezoelectrics are eagerly sought. The quest has been pursued with particular vigour in Japan, where there is a long tradition of expertise in ceramics — PZT itself was developed there at the Tokyo Institute of Technology in the 1950s. The work has tended to focus on other titanates and zirconates, and related perovskite-type oxides such as niobates1. Similar to PZT and its precursor barium titanate, these typically have an asymmetric perovskite crystal structure in which a large metal ion is systematically displaced from its symmetric position, creating spontaneous electrical polarization. In the field-induced flipping of this displacement lies the origin of the piezoelectric behaviour.

In complex mixtures of such oxides, small changes in composition may lead to phase changes that induce piezoelectric and ferroelectric behaviour2. Six years ago a Japanese team discovered a niobate-based system of this sort that showed a very promising piezoelectric response (quantified by the piezoelectric constant d33), especially when prepared in textured polycrystalline form3. There is no lack of other candidates4,5, but none has yet been able to boast a d33 comparable to that of PZT — until now.

Liu and Ren have found that a mixed barium–calcium zirconate–titanate shows a piezoelectric constant in the same range as PZT, and they claim that in theory a single-crystal form of their new material could exceed it by more than threefold6. One of the key questions has been whether such behaviour can be understood sufficiently to enable further refinement by rational design. Liu and Ren think they can explain how the phase behaviour in such systems generally produces a smaller piezoelectric response in lead-free materials, but also how it might be tuned to circumvent this limitation (by introducing a solid-phase triple point) — thereby helping these smart materials become smarter still.