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.

AB O 3 perovskite-type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, or magnetic fi elds. Some solid solutions show remarkably enhanced physical properties including colossal magnetoresistance or giant piezoelectricity. It has been recognized that structural distortions, competing on the local level, are key to understanding and tuning these remarkable properties, yet, it remains a challenge to experimentally observe such local structural details. Here, from neutron pair-distribution analysis, a temperature-dependent 3D atomiclevel model of the lead-free piezoelectric perovskite Na 0.5 Bi 0.5 TiO 3 (NBT) is reported. The statistical analysis of this model shows how local distortions compete, how this competition develops with temperature, and, in particular, how different polar displacements of Bi 3 + cations coexist as a bifurcated polarization, highlighting the interest of Bi-based materials in the search for new lead-free piezoelectrics.

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Hard carbons are the leading candidate anode materials for sodium-ion batteries. However, the sodium-insertion mechanisms remain under debate. Here, employing a novel analysis of operando and ex situ pair distribution function (PDF) analysis of total scattering data, supplemented by information on the local electronic structure provided by operando 23 Na solid-state NMR, we identify the local atomic environments of sodium stored within hard carbon and provide a revised mechanism for sodium storage. The local structure of carbons is well-described by bilayers of curved graphene fragments, with fragment size increasing, and curvature decreasing with increasing pyrolysis temperature. A correlation is observed between the higher-voltage (slope) capacity and the defect concentration inferred from the size and curvature of the fragments. Meanwhile, a larger lower-voltage (plateau) capacity is observed in samples modeled by larger fragment sizes. Operando PDF data on two commercially relevant hard carbons reveal changes at higher-voltages consistent with sodium ions stored close to defective areas of the carbon, with electrons localized in the antibonding π*-orbitals of the carbon. Metallic sodium clusters approximately 13−15 Å in diameter are formed in both carbons at lower voltages, implying that, for these carbons, the lower-voltage capacity is determined by the number of regions suitable for sodium cluster formation, rather than by having microstructures that allow larger clusters to form. Our results reveal that local atomic structure has a definitive role in determining storage capacity, and therefore the effect of synthetic conditions on both the local atomic structure and the microstructure should be considered when engineering hard carbons.

Electron microscopy and diffraction are used to examine the nanoscale structure and molecular orientation in molecular films down to nominally monolayer thickness. The films studied consist of the planar n-type molecular semiconductor copper hexadecafluorophthalocyanine (F16CuPc) directly deposited onto graphene oxide (GO) membranes by organic molecular beam deposition. The graphene oxide support crucially provides the strength and low background required to analyze the crystal structure and morphology of even nominally monolayer thick films and is of relevance for molecular electronic applications. The crystal structure of the F16CuPc polymorph is solved by X-ray diffraction of single crystals and used to analyze the electron diffraction patterns from the thin-films, revealing that the F16CuPc molecules assemble with their molecular plane oriented perpendicular to the GO. There is no evidence for changes in the unit cell with film thickness, although the thinnest films show the greatest disorder in molecular packing. Direct deposition of molecular materials on low contrast and relevant substrates combined with electron and scanning probe microscopy is thus shown to be a powerful technique for elucidating structure in nanostructured organic thin films.

Metal-organic framework (MOF) glasses have become a subject of interest as a distinct category of melt quenched glass, and have potential applications in areas such as ion transport and sensing. In this paper we show how MOF glasses can be combined with inorganic glasses in order to fabricate a new family of materials composed of both MOF and inorganic glass domains. We use an array of experimental techniques to propose the bonding between inorganic and MOF domains, and show that the composites produced are more mechanically pliant than the inorganic glass itself.