The temperature-composition phase diagram of barium calcium titanate zirconate, (x(Ba 0.7 Ca 0.3 TiO 3 )-(1-x)(BaZr 0.2 Ti 0.8 O 3 ); BCTZ) has been reinvestigated using high-resolution synchrotron x-ray powder diffraction. Contrary to previous reports of an unusual rhombohedral-tetragonal phase transition in this system, we have observed an intermediate orthorhombic phase, isostructural to that present in the parent phase, BaTiO 3 , and we identify the previously assigned T-R transition as a T-O transition.We also observe the O-R transition coalescing with the previously observed triple point, forming a phase convergence region. The implication of the orthorhombic phase in reconciling the exceptional piezoelectric properties with the surrounding phase diagram is discussed.Lead oxide based ferroelectric materials such as lead zirconate titanate (PbZr 1-x Ti x O 3 , PZT) are the most widely used piezoelectrics, because of their excellent properties. The microstructural origin of the remarkable piezoelectric properties remained puzzling for several decades, it was quickly recognized however that the complex structural phase diagram was key. In particular, it has been recognized that piezoelectric properties are maximized close to the structural phase transition from rhombohedral (R) to tetragonal (T) phases, which exists in a limited range of chemical composition:the so called morphotropic phase boundary (MPB). 1 These R and T phases do not have a 2 crystallographic group-subgroup relationship, and thus no continuous transition between them is possible. A breakthrough in the understanding of the remarkable piezoelectric properties of PZT was achieved by showing that the strong piezoelectric properties of these solid solutions can be interpreted via a 'polarisation rotation' between the adjacent R-and T-phases through one (or more) intermediate monoclinic phases 2,3 . Subsequent work on other lead-containing piezoelectrics such as PMN-PT or PZN-PT has further underlined the need for knowledge of structural phase diagrams for both the understanding of remarkable properties, and the design of new improved piezoelectrics (see reviews 4-7 ).In recent years, the environmental and health hazards of lead have been recognized, so that recycling and disposal of devices containing lead-based piezoelectric materials became of great concern. As a consequence, there is an increasing interest in the development of lead-free piezoelectric materials [8][9][10][11][12][13] with the main challenge to develop materials with an equivalent or even -on both ceramics and thin film samples (e.g. [15][16][17][18][19][20] ). The first structural phase diagram of BCTZ has been reported 14 and the different phase sequences with increasing temperature can be summarized as follows: (i) x ≤ 0.32: a single phase transition is observed from the low temperature R-phase to the high-temperature prototype cubic ̅ structure (C), (ii) 0.32 < x < 0.8 : presence of two phase transitions through a R-T-C phase sequence and (iii) x > 0.8: a single phase tran...

(PZT) is one of the most important and widely used piezoelectric materials. The study of its local and average structures is of fundamental importance in understanding the origin of its high-performance piezoelectricity. Pair distribution function analysis and Rietveld refinement have been carried out to study both the short-and long-range order in the Zr-rich rhombohedral region of the PZT phase diagram. The nature of the monoclinic phase across the Zr-rich and morphotropic phase boundary area of PZT is clarified. Evidence is found that long-range average rhombohedral and both long-and short-range monoclinic regions coexist at all compositions. In addition, a boundary between a monoclinic (M A ) structure and another monoclinic (M B ) structure has been found. The general advantage of a particular monoclinic distortion (M A ) for high piezoactivity is discussed from a spatial structural model of susceptibility to stress and electric field, which is applicable across the wide field of perovskite materials science.

The synthesis of four novel crystalline zeolitic imidazolate framework (ZIF) structures using a mixed-ligand approach is reported. The inclusion of both imidazolate and halogenated benzimidazolate-derived linkers leads to glass-forming behavior by all four structures. Melting temperatures are observed to depend on both electronic and steric effects. Solid-state NMR and terahertz (THz)/Far-IR demonstrate the presence of a Zn-F bond for fluorinated ZIF glasses. In situ THz/Far-IR spectroscopic techniques reveal the dynamic structural properties of crystal, glass and liquid phases of the halogenated ZIFs, linking the melting behavior of ZIFs to the propensity of the ZnN4 tetrahedra to undergo thermally-induced deformation. The inclusion of halogenated ligands within MOFglasses improves their gas uptake properties.