(NBT), BaTiO 3 (BTO), and K 0.5 Bi 0.5 TiO 3 (KBT) are known but all have inferior properties to PZT. [ 2,3,5 ] Bi 3+ has a 6s 2 confi guration with crystal chemistry similar to that of Pb 2+ , and bismuthbased perovskites are attractive as they can offer high Curie and depolarization temperatures required for demanding application environments. [ 5,6 ] [ 9 ] which can be converted into a long-range polarization along this direction by the introduction of LaFeO 3 (LFO) which itself has antiferrodistortive [110] p displacements, although this orthorhombic O [110] The perovskite oxide lead zirconate titanate (PbZr 1− x Ti x O 3 ) (PZT) has extraordinary electromechanical properties at the morphotropic phase boundary (MPB), [ 1 ] making modifi ed PZT ceramics the basis for almost all actuators, sensors and related applications in use today. The MPB in the PZT solid solution occurs near x ≈ 0.48 [ 1 ] between the ferroelectric rhombohedral ( R 3 m , denoted as R [111] ) and tetragonal ( P 4 mm , denoted as T [001] ) phases, with polarizations lying along the [111] p body diagonal and [001] p edge of the primitive ≈ 4 Å ABO 3 perovskite unit cell, respectively. [1][2][3] The PZT phases are untilted and the R [111] and T [001] structures are described crystallographically, using a modifi ed Glazer notation, as a a a + , respectively, where the subscript indicates ferroelectric displacement and the superscript the nature of the octahedral tilting with respect to the primitive unit cell axes. [ 4 ] It is challenging to create an MPB in a bismuth-based lead-free system as it has proved diffi cult to prepare phases with polarization directed along the [001] p primitive cell edge in such materials. Several Pb-free MPB systems based on K 0.5 Na 0.5 NbO 3 , Na 0.5 Bi 0.5 TiO 3

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Currently available high performance piezoelectric materials, predominantly based on lead zirconate titanate (PZT), are typically limited to operating temperatures of around 200 °C or below. There are many applications in sectors such as automotive, aerospace, power generation and process control, oil and gas, where reliable operation at higher temperatures is required for sensors, actuators and transducers. New materials are being actively developed to meet this need. Development and application of new and existing materials requires reliable measurement of their properties under these challenging conditions. This paper reviews the current state of the art in measurement of piezoelectric properties at high temperature, including direct and converse piezoelectric measurements and resonance techniques applied to high temperature measurements. New results are also presented on measurement of piezoelectric and thermal expansion and the effects of sample distortion on piezoelectric measurements. An investigation of the applicability of resonance measurements at high temperature is presented, and comparisons are drawn between the results of the different measurement techniques. New results on piezoelectric resonance measurements on novel high temperature piezoelectric materials, and conventional PZT materials, at temperatures up to 600 °C are presented.

The in situ X-ray Pair Distribution Function (PDF) characterisation technique has been used to study the behaviour of (K x Na 1-x ) 0.5 Bi 0.5 TiO 3 , as a function of electric field. As opposed to conventional X-ray Bragg diffraction techniques, PDF is sensitive to local atomic displacements, detecting local structural changes at the Ångstrom to nanometre scale. Several field-dependent ordering mechanisms can be observed in x = 0.15, 0.18 and at the morphotropic phase boundary (MPB) composition x = 0.20. X-ray total scattering shows suppression of diffuse scattering with increasing electric field amplitude, indicative of an increase in structural ordering. Analysis of PDF peaks in the 3-4 Å range shows ordering of Bi-Ti distances parallel to the applied electric field, illustrated by peak amplitude redistribution parallel and perpendicular to the electric field vector. A transition from ‹110› to ‹112› type off-centre displacements of Bi relative to the neighbouring Ti atoms are observable with increasing x. Analysis of PDF peak shift with electric field show the effects of Bi-Ti 2 redistribution and onset of piezoelectric lattice strain. The combination of these field-induced ordering mechanisms is consistent with local redistribution of Bi-Ti distances associated with domain reorientation and an overall increase in order of atomic displacements.

BiFeO3)-(PbTiO3) is a ferroelectric material, 80 (101) that also demonstrates anti-ferromagnetism with weak 60 (111) 6040 BFPT ferromagnetism, at room temperature. The morphotropic 40 ( X X/2) phase boundary composition, 0.7BiFeO3-0.3PbTiO3, 20 exhibits a ferroelectric Tc of 635°C and a TN of 287°C. 0 Presented here is a study of the ferromagnetic transition vs. composition, measured using neutron diffraction and 8-magnetisation from AC susceptibility, as a function of 60 6535 BFPT temperature on sintered polycrystalline materials. The 40 antiferromagnetic transition is observed to occur at 20 significantly higher temperatures than previously 0 ___ reported. For 0.7BiFeO3 -0.3PbTiO3 a Neel temperature + of 3300C is recorded. @ 80 -Neutron data also indicates that TN is much less dependant -60 7030 BFPT on composition than previously documented. 40 20 1