Starting with the history of the fundamental science of the relation of structure to composition delineated completely by Goldschmidt, we use the perovskite structure to illustrate the enormous power of crystal chemistry-based intelligent synthesis in creating new materials.The perovskite structure is shown to be the single most versatile ceramic host. By appropriate changes in composition one can modify the most significant electro- ceramic dielectric (BaTiO3 and its relatives) phase in industry, into metallic conductors, superconductors or the highest pressure phases in the earth. After an historical introduction of the science, detailed treatment of the applications is confined to the most recent research on novel uses in piezoelectric, ferroelectric and related applications.

High resolution x-ray powder diffraction measurements on poled ${\mathrm{PbZr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ (PZT) ceramic samples close to the rhombohedral-tetragonal phase boundary (the so-called morphotropic phase boundary) have shown that for both rhombohedral and tetragonal compositions the piezoelectric elongation of the unit cell does not occur along the polar directions but along those directions associated with the monoclinic distortion. This work provides the first direct evidence for the origin of the very high piezoelectricity in PZT.

The perovskitelike ferroelectric system ${\mathrm{PbZr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ (PZT) has a nearly vertical morphotropic phase boundary (MPB) around $x=0.45\mathrm{}–\mathrm{0.50.}$ Recent synchrotron x-ray powder diffraction measurements by Noheda et al. [Appl. Phys. Lett. 74, 2059 (1999)] have revealed a monoclinic phase between the previously established tetragonal and rhombohedral regions. In the present work we describe a Rietveld analysis of the detailed structure of the tetragonal and monoclinic PZT phases on a sample with $x=0.48\mathrm{}$ for which the lattice parameters are, respectively, $a_t=4.044\mathrm{}$ Å, $c_t=4.138\mathrm{}$ Å, at 325 K, and $a_m=5.721\mathrm{}$ Å, $b_m=5.708\mathrm{}$ Å, $c_m=4.138\mathrm{}$ Å, $\beta =90.496\mathrm{}°,$ at 20 K. In the tetragonal phase the shifts of the atoms along the polar [001] direction are similar to those in ${\mathrm{PbTiO}}_3$ but the refinement indicates that there are, in addition, local disordered shifts of the Pb atoms of $\sim 0.2$ Å perpendicular to the polar axis. The monoclinic structure can be viewed as a condensation along one of the $〈110〉$ directions of the local displacements present in the tetragonal phase. It equally well corresponds to a freezing-out of the local displacements along one of the $〈100〉$ directions recently reported by Corker et al. [J. Phys.: Condens. Matter 10, 6251 (1998)] for rhombohedral PZT. The monoclinic structure therefore provides a microscopic picture of the MPB region in which one of the “locally” monoclinic phases in the “average” rhombohedral or tetragonal structures freezes out, and thus represents a bridge between these two phases.

Recent structural studies of ferroelectric ${\mathrm{PbZr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ (PZT) with $x=0.48,$ have revealed a monoclinic phase in the vicinity of the morphotropic phase boundary (MPB), previously regarded as the boundary separating the rhombohedral and tetragonal regions of the PZT phase diagram. In the present paper, the stability region of all three phases has been established from high-resolution synchrotron x-ray powder-diffraction measurements on a series of highly homogeneous samples with $0.42<~x<~\mathrm{0.52.}$ At 20 K, the monoclinic phase is stable in the range $0.46<~x<~0.51,$ and this range narrows as the temperature is increased. A first-order phase transition from tetragonal to rhombohedral symmetry is observed only for $x=\mathrm{0.45.}\mathrm{}$ The MPB, therefore, corresponds not to the tetragonal-rhombohedral phase boundary, but instead to the boundary between the tetragonal and monoclinic phases for $0.46<~x<~\mathrm{0.51.}$ This result provides important insight into the close relationship between the monoclinic phase and the striking piezoelectric properties of PZT; in particular, investigations of poled samples have shown that the monoclinic distortion is the origin of the unusually high piezoelectric response of PZT.

The polarization and strain behavior of $\mathrm{Ba}({\mathrm{Ti}}_{\text{1−x}}{\mathrm{Zr}}_x){\mathrm{O}}_3$ $\text{(x=0–0.3)}$ ceramics are studied. The unipolar strain levels of ∼0.18% at 40 kV/cm and of ∼0.25% at ∼120 kV/cm with small hysteresis were obtained for the ceramics with $\text{0.03⩽x⩽0.08.}$ The remnant polarization is ∼13–18 μC/cm² for $\text{0.03⩽x⩽0.08}$ and below 2 μC/cm² for $\text{0.15⩽x⩽0.3}$ at room temperature. The electromechanical coupling coefficient $K_{33}\text{=56.5\%}$ and the piezoelectric stain coefficient $d_{33}\text{=236\hspace{0.17em}}\mathrm{pC/N}$ were obtained for the ceramics with $\text{x=0.05.}$ These results indicated that the $\mathrm{Ba}({\mathrm{Ti}}_{\text{1−x}}{\mathrm{Zr}}_x){\mathrm{O}}_3$ system is a promising lead-free high strain material for applications.

In this study, the phase transition behavior of the ${\mathrm{BaTiO}}_{\mathrm{3}}{\mathrm{–BaZrO}}_3$ system was studied using micro-Raman scattering and dielectric measurement techniques. ${\mathrm{BaZr}}_x{\mathrm{Ti}}_{\text{1−x}}{\mathrm{O}}_3$ ceramics were prepared for $\text{x=0.00,}$ 0.05, 0.08, 0.15, 0.20, and 1.00 compositions using a solid-state reaction technique. A single-phase perovskite structure of the ceramics was identified by the x-ray diffraction technique. The basic phase transition temperatures in these compositions were studied in the temperature range of 70–575 K. The tetragonal to cubic transition temperature was found to decrease with increasing Zr content. The orthorhombic to tetragonal transition temperature that increases with an initial increase in Zr content merges with the tetragonal–cubic transition for $\text{x⩾0.15}$ compositions. Raman spectra of rhombohedral and orthorhombic phases could not be distinguished. Excellent agreement between the crystallographic transition temperatures obtained by both techniques suggested that Zr substituted octahedra were uniformly distributed in the material without introducing any mechanical stress.