A first-principles-derived approach is developed to study finite-temperature properties of Pb(Zr1−xTix)O3 (PZT) solid solutions near the morphotropic phase boundary (MPB). Structural and piezoelectric predictions are in excellent agreement with experimental data and direct first-principles results. A low-temperature monoclinic phase is confirmed to exist, and is demonstrated to act as a bridge between the well-known tetragonal and rhombohedral phases delimiting the MPB. A successful explanation for the large piezoelectricity found in PZT ceramics is also provided. PACS:77.84.Dy,81.30.Bx,77.65.Bn Ferroelectric perovskite A(B ′ B ′′)O 3 alloys are of growing importance for a variety of device applications [1,2], and are also of great current fundamental interest since little is known about the effects responsible for their anomalous properties. A good example of an A(B ′ ,B ′′)O 3 solid solution that is of both fundamental and technological importance is the Pb(Zr 1−x Ti x)O 3 system. Usually denoted as PZT, this mixed-cation alloy is currently in widespread use in piezoelectric transducers and actua-tors [1]. Its phase diagram exhibits a morphotropic phase boundary (MPB) separating a region with a tetragonal ground state (x > 0.52) from a region with rhombohedral symmetry (x < 0.45) [3]. High piezoelectric response is experimentally found in ceramics of PZT around the MPB. The origins of this large piezoelectric response are unclear. On the one hand, semi-empirical simulations predict that the large experimental value of the d 33 piezoelectric coefficient results mainly from the large value of d 33 that a single-crystal PZT would exhibit [4]. On the other hand, recent first-principles calculations [5,6] have found that the d 33 coefficient of a tetragonal single crystal of Pb(Zr 0.5 Ti 0.5)O 3 are estimated to be three times smaller than the experimental value obtained for ceramics at low temperature. Furthermore, recent synchrotron x-ray powder diffrac-tion studies have revealed the existence of an unexpected low-temperature monoclinic phase of PZT at x=0.48 [7], which implies that the phase diagram of PZT is more complex than previously thought. This monoclinic phase may act as a second-order transitional bridge between the tetragonal phase, for which the electrical polarization P lies along the pseudo-cubic [001] direction, and the rhom-bohedral phase, for which P is along the pseudo-cubic [111] direction. If this is indeed the case, the polarization of the monoclinic phase continuously rotates as the composition x decreases in the MPB region [7]. Such a continuous rotation has yet to be observed. Obviously, accurate simulations are needed to understand the properties of perovskite alloys in general, and of PZT in particular. Since the beginning of the present decade, first-principles methods have emerged as a powerful tool for investigating properties of ferroelectric systems theoretically (see [5,6,8,9] and references therein). However, these methods are essentially restricted to the study of the zero-temper...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.