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The prohibition of lead in many electronic components and devices due to its toxicity has reinvigorated the race to develop substitutes for lead zirconate titanate (PZT) based mainly on the potassium sodium niobate (KNN) and sodium bismuth titanate (NBT). However, before successful transition from laboratory to market, critical environmental assessment of all aspects of their fabrication and development must be carried out in comparison with PZT. Given the recent findings that KNN is not intrinsically ‘greener’ than PZT, there is a tendency to see NBT as the solution to achieving environmentally lead-free piezoelectrics competitive with PZT. The lower energy consumed by NBT during synthesis results in a lower overall environmental profile compared to both PZT and KNN. However, bismuth and its oxide are mainly the by-product of lead smelting and comparison between NBT and PZT indicates that the environmental profile of bismuth oxide surpasses that of lead oxide across several key indicators, especially climate change, due to additional processing and refining steps which pose extra challenges in metallurgical recovery. Furthermore, bismuth compares unfavourably with lead due to its higher energy cost of recycling. The fact that roughly 90–95% of bismuth is derived as a by-product of lead smelting also constitutes a major concern for future upscaling. As such, NBT and KNN do not offer absolute competitive edge from an environmental perspective in comparison to PZT. The findings in this work have global practical implications for future Restriction of Hazardous Substances (RoHS) legislation for piezoelectric materials and demonstrate the need for a holistic approach to the development of sustainable functional materials. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Since their invention in the late 1960s, glass ionomer cements (GICs) have been used extensively in dentistry but recently they have also been utilised in ear nose and throat (ENT) surgery. Unfortunately, Al3+, a component of conventional ionomer glasses, has been linked to poor bone mineralisation and neurotoxicity. Objective: The aim of the research was to modify a commercial ionomer glass composition by substituting Al2O3 with Fe2O3. Methods: Glasses with the following molar compositions were fabricated: 4.5SiO2·3M2O3·XP2O5·3CaO·2CaF2 (M=Al or Fe, X=0–1.5). The glasses were characterised using X-ray fluorescence (XRF) and X-ray powder diffraction (XRD). Cements were prepared using a standard ratio of; 1g of glass powder: 0.2g of dried polyacrylic acid: 0.3g of 10% tartaric acid solution. Cement formation was assessed using a Gilmore needle and in vitro biocompatibility was investigated for novel cement formulations. Results: XRF revealed that the Fe2O3-based glasses had Al2O3 contamination from the crucibles and also had undergone substantial F− losses. XRD gave peaks that corresponded to magnetite Fe3O4 (JCPDS # 19-629) in all compositions. Apatite Ca5(PO4)3(OH,F) (JCPDS # 15-876) was identified in P2O5 containing glasses. It was possible to fabricate cements from all of the Fe2O3-based ionomer glasses. Good in vitro biocompatibility was observed for the Fe2O3-based cements. Conclusion: Ionomer glasses may be prepared by entirely replacing Al2O3 with Fe2O3. Cement setting times appeared to be related to P2O5 content. Fe2O3-based cements showed good in vitro biocompatibility. [Copyright &y& Elsevier]

Abstract: Solid solutions of (x)Re(Co1/2Ti1/2)O3–(1− x)CaTiO3 (Re=La and Nd, abbreviated to xLCT and xNCT, respectively) where x =0, 0.25, 0.5, 0.75 and 1 have been fabricated using solid state synthesis. Samples have been examined using X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM) and their dielectric properties measured at microwave (MW) frequencies. Formation of single phase solid solutions were confirmed by XRD and the measured lattice parameters varied linearly from LCT (a =5.66Å, b =7.867Å and c =5.494Å) and NCT (a =5.636Å, b =7.914Å and c =5.461Å) to CT (a =5.596Å, b =7.731Å and c =5.424Å). XRD and TEM confirmed both in-phase and antiphase rotations of O-octahedra consistent with an a − a − c + tilt system across the entire solid solution series. Electron diffraction revealed that LCT and NCT have reflections associated with B-site cation ordering which is absent for x ≤0.75. MW dielectric measurements showed that LCT and NCT were highly insulating with microwave quality factor (Qf 0) values of 39,000 and 34,000, respectively. Compositions anticipated to have a zero temperature coefficient of resonant frequency (τ f) are 0.48LCT-CT and 0.52NCT-CT with ɛ r =45 and Qf 0 ∼5000 and ɛ r =43 and Qf 0 ∼4000, respectively. [Copyright &y& Elsevier]

Abstract: The microstructures of 8 model Ag-based electrode pastes, fired on to PZT using commercial firing schedules, have been examined using SEM with EDS, and the electrical performance of these systems investigated. The effects of three different bonding additives (Bi2O3, CuO, and a lead boro-aluminosilicate glass frit) were investigated both individually and together. The additives were found to be vital for good bonding. In unfritted systems eutectic reactions between the additives, the electrode Ag, and the PZT dominated the microstructural evolution, the loss of Pb from the ceramic being of particular importance. In fritted pastes the glass frit dissolved the Bi2O3, and was able to draw the CuO to the interface, allowing reaction to occur. Electrical testing showed the unfritted systems to exhibit increased dielectric losses at frequencies <10,000Hz due to Pb loss resulting in interfacial polarisation. [Copyright &y& Elsevier]

0.9Ba([Zn0.60Co0.40]1/3Nb2/3)O3–0.1Ba(Ga0.5Ta0.5)O3 (BCZN–BGT) ceramic resonators (quality factor, Q=32,000 at the rate of 3.05 GHz, relative permittivity, #x03B5;r=35 and temperature coefficient of the resonant, τf=0) have been fabricated which are suitable in terms of cost and performance for base stations supporting third generation architecture. The new compounds are perovskite structured (a=4.09 Å) but exhibit no superlattice reflections at any heat treatment temperature according to X-ray diffraction (XRD). However, annealing and quenching of samples followed by transmission electron microscopy and Raman spectroscopy revealed an order–disorder phase transition at ∼1200 °C. Annealing below this temperature (1100 °C) gave rise to discrete ±1/3{h k l}p and diffuse 1/2{h k l}p superlattice reflections in the same 〈1 1 0〉p zone axis electron diffraction patterns and the presence of F2g and A1g modes in Raman spectra. It is proposed that ±1/3{h k l}p reflections result from 1:2 long-range ordered domains of BCZN whereas the diffuse 1/2{h k l}p reflections arise from short range fcc ordered BGT rich regions at the 1:2 domain boundaries. A short-range ordered fcc superlattice was observed in samples quenched from above the order–disorder phase transition (>1200 °C) which was accompanied by the presence of only the A1g mode in Raman spectra. [Copyright &y& Elsevier]

Single phase, dense La(Co1/2Ti1/2)O3 (LCT) ceramics have been fabricated using conventional solid state synthesis. Samples were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and their dielectric properties were studied at radio and microwave frequencies. X-ray and electron diffraction conclusively revealed that LCT contained in-phase and antiphase rotations of the O-octahedra, consistent with and a-a-c+ tilt system in the Glazer classification. However, XRD indicated that the Co and Ti ions were disordered on the B-site whereas TEM and Raman spectroscopy exhibited reflections and modes which suggested that partial ordering may be present. Moreover, some Raman bands could only be explained by assuming that at least some of the octahedra exhibited a Jahn–Teller distortion. Dielectric measurements indicated that LCT is insulating with low dielectric loss, 0.0024 at 1 MHz and frequency independent relative permittivity, #x03B5;r=25. A quality factor, Q×fo=38,000 was obtained at microwave frequencies along with a temperature coefficient of the resonant frequency, TCF=-42 MK-1. [Copyright &y& Elsevier]

Ordering of the B-site cations in UMTS (universal mobile telecommunications systems) standard resonator pucks composed of perovskite structured, 0.95BaZn1/3Ta2/3O3–0.05SrGa1/2Ta1/2O3 (BZT–SGT) has been investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and powder neutron diffraction (PND). XRD patterns from samples sintered at 1550 °C/2 h but annealed and quenched at 50 °C intervals between 1400 and 1600 °C revealed that the order–disorder phase transition was at ∼1500 °C. In addition, a peak at ∼29.5° 2θ attributed to a Ba8ZnTa6O24 phase was present due to ZnO loss. Electron diffraction patterns revealed that samples heat treated &ges;1500 °C (including as sintered samples, 1525 °C/2h,) exhibited short-range 1:2 ordering along all <111> directions giving rise to an average short-range face centred cubic structure. Samples annealed and quenched from below 1500 °C showed 1:2 order. To avoid excessive ZnO loss, an annealing temperature was chosen at 1275 °C (for 24 and 168 h). Neutron diffraction data were best refined using two ordered BZT phases with slightly different lattice parameters. TEM revealed a microstructure in each case consisting of 1:2 small ordered domains in the centre of all grains but with every second grain exhibiting a concentric shell composed of an ordered single domain, containing elongated translational (APBs) but not orientational domains. The formation of the concentric ordered shell was attributed to grain boundary migration during grain growth. As-sintered samples gave unloaded quality factors (Q)=54,000 at 2 GHz which rose to 78,000 at 2 GHz after annealing for 24 h. No further improvement in Q was observed for longer annealing times. [Copyright &y& Elsevier]

The effects of devitrification of an ionomer glass with a molar composition 4.5SiO2·3Al2O3·1.5P2O5·3CaO·2CaF2 on cement formation and in vitro biocompatibility were investigated. Differential thermal analysis was used to study the phase evolution in the glass, and to determine the heat treatments for production of glass-ceramics. X-ray diffraction patterns from glass frit heat-treated at 750°C for 2 h contained peaks corresponding to apatite (JCPDS 15-876), whereas for samples heat-treated at 950°C for 2 h apatite and mullite (JCPDS 15-776) were the major phases detected. Transmission electron microscopy (TEM) confirmed that apatite and apatite–mullite phases were present after heat treatments at 750°C and 950°C respectively. Glass and glass-ceramics were ground to prepare <45 μm powders and glass ionomer cements were produced using a ratio of 1 g powder: 0.2 g PAA: 0.3 g 10% m/v tartaric acid solution in water. In vitro biocompatibility was evaluated using cultured rat osteosarcoma (ROS) cells. Scanning electron microscopy (SEM) showed that cells colonised the surfaces of cements prepared using untreated ionomer glass and glass crystallised to form apatite (750°C/2 h). However, quantitative evaluation using MTT and total protein assays indicated that more cell growth occurred in the presence of cements prepared using ionomer glasses crystallised to apatite than cements prepared using untreated glass. The least cell growth and respiratory activity was observed on cements made with crystallised glass containing both apatite and mullite. It was concluded that the controlled devitrification of ionomer glasses could be used to produce GIC bone cements with improved biocompatibility. [Copyright &y& Elsevier]

Ceramic honeycomb extrusion is a technique capable of attaining high strength, porous ceramics. However, challenges prevent the realisation of its potential. These include the design of an intricate honeycomb die and the formulation of an extrudable paste. The present study addresses the latter by using guar gum (GG) as a binder. GG was rationally selected because hydrogels thereof exhibit strong shear-thinning and high stiffness properties, which are required for extrusion. Rheological analyses demonstrated ceramic pastes with similar qualities were achieved, with hydroxyapatite (HA) used as the model ceramic. The shear stiffness modulus of HA pastes was determined as 8.4 MPa with a yield stress of 1.1 kPa. Moreover, this was achieved with GG as the sole additive, which further facilitates the overall fabrication process. The binder extraction notably occurred at relatively low temperatures when other high molecular weight polymers demand temperatures above 1000 °C; therefore the latter precludes the use of ceramics with low sintering onset. The process culminated in a porous HA scaffold with similar porosity to that of a commercial HA graft, but with higher compressive strength. Lastly, the study notes that the biological and water-soluble properties of GG can broaden its application into other ceramic fabrication processes. [ABSTRACT FROM AUTHOR]

Solar cells are considered as one of the prominent sources of renewable energy suitable for large-scale adoption in a carbon-constrained world and can contribute to reduced reliance on energy imports, whilst improving the security of energy supply. A new arrival in the family of solar cells technologies is the organic-inorganic halide perovskite. The major thrust for endorsing these new solar cells pertains to their potential as an economically and environmentally viable option to traditional silicon-based technology. To verify this assertion, this paper presents a critical review of some existing photovoltaic (PV) technologies in comparison with perovskite-structured solar cells (PSCs), including material and performance parameters, production processes and manufacturing complexity, economics, key technological challenges for further developments and current research efforts. At present, there is limited environmental assessment of PSCs and consequently, a methodologically robust and environmentally expansive lifecycle supply chain assessment of two types of PSC modules A and B is also undertaken within the context of other PV technologies, to assess their potential for environmentally friendly innovation in the energy sector. Module A is based on MAPbX 3 perovskite structure while module B is based on CsFAPbX 3 with improved stability, reproducibility and high performance efficiency. The main outcomes, presented along with sensitivity analysis, show that PSCs offer more environmentally friendly and sustainable option, with the least energy payback period, as compared to other PV technologies. The review and analysis presented provide valuable insight and guidance in identifying pathways and windows of opportunity for future PV designs towards cleaner and sustainable energy production. [ABSTRACT FROM AUTHOR]

Microcracking in YMnO3 ceramics originates from a combination of 3.7% volume change and strong anisotropy in the thermal expansion coefficient of the hexagonal structure. In this paper, the effect of Ti doping on the microstructure, structure and dielectric response of YMnO3 ceramics is studied. Lattice anisotropy of the hexagonal cell markedly decreased with increasing Ti, reducing the residual stresses created at the high-temperature phase transition and commensurately decreasing the crack density (3.2vol.% YMnO3 to 0.9vol.% YMn0.9Ti0.1O3). These results represent the first systematic work to reduce microcracking in YMnO3-based ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Microwave dielectric ceramics in the Sr1−x Ca x La4Ti5O17 (0≤ x ≤1) composition series were prepared through a solid state mixed oxide route. All the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1450–1580°C. Theoretical density and molar volume decreased due to the substitution of Ca2+ for Sr2+ which was associated with a decrease in the dielectric constant (ɛ r) and temperature coefficient of resonant frequency (τ f) but an increase in quality factor, Qf o. Optimum properties were achieved for Sr0.4Ca0.6La4Ti5O17 which exhibited, ɛ r ∼53.7, Qf o ∼11,532GHz and τ f ∼−1.4ppm/°C. [Copyright &y& Elsevier]

The rising cost of energy and concerns about the environmental impact of manufacturing processes have necessitated the need for more efficient and sustainable manufacturing. The ceramic industry is an energy intensive industrial sector and consequently the potential to improve energy efficiency is huge, particularly through the introduction of modern sintering technologies. Although several energy efficient sintering processes have been developed, there is no comprehensive techno-economic analysis which compares and contrasts these techniques. This paper presents a critical review and analysis of a number of sintering techniques and compares them with the recently developed cold sintering process (CSP), including mode of operation, sintering mechanism, typical heating rates, duration of sintering, energy consumption profile and energy saving potential, limitations, key challenges for further development and current research efforts. By using a figure of merit, pounds per tonne of CO 2 saved (£/tCO 2 -eq), which links initial capital investment with energy savings, within a framework derived from ranking principles such as marginal abatement cost curves and Pareto optimisation, we have demonstrated that under the scenarios considered for 3 separate functional oxides ZnO, PZT and BaTiO 3 , CSP is the most economically attractive sintering option, indicating lower capital costs and best return on investment as well as considerable energy and emission savings. Although the current work establishes the viability of CSP as a competitive and sustainable alternative to other sintering techniques, the transition from laboratory to industry of CSP will require hugely different facilities and instrumentation as well as relevant property/performance validation to realise its full potential. [ABSTRACT FROM AUTHOR]

The molten salt method was used to synthesise the MAX phase compounds Ti 2 AlC and Ti 3 AlC 2 from elemental powders. Between 900–1000 °C, Ti 2 AlC was formed alongside ancillary phases TiC and TiAl, which decreased in abundance with increasing synthesis temperature. Changing the stoichiometry and increasing the synthesis temperature to 1300 °C resulted in formation of Ti 3 AlC 2 alongside Ti 2 AlC and TiC. The type of salt flux used had little effect on the product formation. The reaction pathway for Ti 2 AlC was determined to be the initial formation of TiC 1-x templating on the graphite and titanium aluminides. [ABSTRACT FROM AUTHOR]

A reliable method of extracting core-volume fraction from TEM micrographs of core-shell polycrystalline microstructures is presented. Three commonly used averaging methods based on a simple spherical model are shown to consistently underestimate the core-volume fraction due to the interpretation of a 3D structure from a 2D slice. The same trend is also revealed using Voronoi tessellated structures to mimic polycrystalline ceramics. In some cases the underestimate is less than half the true core-volume fraction. We show that using a new maximum core-volume fraction methodology can improve the extracted value to a consistent error of less than 5%. This approach uses a value taken from the largest core-volume fraction measured from 10 grains that exhibit a core-shell microstructure. This provides increasing accuracy and improvements in the confidence of the measurement when extracting core-volume fractions of polycrystalline ceramics from 2D TEM micrographs. [ABSTRACT FROM AUTHOR]

Abstract: The high throughput synthesis of BiFeO3 and rare earth doped BiFeO3 films using a modified molecular beam epitaxy technique is reported. Optimum conditions for deposition have been established and compositionally graded Bi(1− x)Nd x FeO3 (x =0.08 to 0.24) thin films have been fabricated on platinised silicon substrate (Si/SiO2/TiO2/Pt) with the aim of finding the optimum Nd dopant concentrations for enhanced piezoelectric properties. For x <0.12, the structure and symmetry were identical to that of the R3c BiFeO3 end member. For x >0.20, the structure and symmetry were consistent with the NdFeO3 end member (Pnma). For compositions 0.12< x <0.2, a gradual transition from R3c to Pnma was observed via a mixed phase region but no compositional interval could be unambiguously identified in which the intermediate PbZrO3-like structure, reported by Karimi et al. (2009) [6], existed as a single phase. Piezoresponse force microscopy remanent hysteresis measurements of the film revealed a statistical increase in the piezoelectric response at x ≈0.11 within the R3c region adjacent to the mixed phase field. [Copyright &y& Elsevier]

Abstract: Ceramics of xBiFeO3-(1−x)(K0.5Bi0.5)TiO3 (where x=0.6, 0.7 and 0.8) have been produced, and characterized using neutron diffraction, revealing a G-type antiferromagnetic structure. The ferroelectric Curie temperature was >430°C, and the Néel temperature was in the range 228–254°C, increasing with x. Ferroelectricity was confirmed using strain and polarization-field measurements, for the composition x=0.6, with a P s=26μC/cm2 and a coercive field=3.85kV/mm. Piezoelectricity was observed for this material with a low-field d 33 of 37pm/V, and a high-field d 33 ⁎ of 80pm/V where x=0.6. The reduction in coercive field in this system is shown to correlate with the oxygen octahedral tilt angle. The solid solution xBiFeO3-(1−x)(K0.5Bi0.5)TiO3 has potential as a high temperature, piezoelectric, multiferroic system. [Copyright &y& Elsevier]

Bi(Fe0.5Sc0.5)O3–PbTiO3 (BSFPT) films have been fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. The microstructure, chemical state, ferroelectric and magnetic properties were investigated. The leakage mechanism of the BSFPT thin film showed bulk limited, space charge limited current characteristics from 200 to 220K, whereas bulk limited Poole–Frenkel emission and interface limited Fowler–Nordheim tunneling coexisted at temperatures between 250 and 300K. The substitution of Sc3+ for Fe3+ ions was considered to improve the valence stability and, therefore, decrease the overall leakage current. [ABSTRACT FROM AUTHOR]

Abstract: The structure–property relations of Mg-doped SrTiO3 (ST) sol–gel thin films deposited on Pt/TiO2/SiO2/Si substrates have been investigated in order to determine the effect that Mg dopants have on the dielectric properties of SrTiO3. It has been predicted that Mg-doped SrTiO3 should exhibit a dielectric anomaly similar to that observed recently in Bi doped SrTiO3 but, to date, no polar state has been reported. It has been suggested that this may relate to the low solubility of Mg on the A-site in bulk ceramics (<0.05at.%). However, for Sr1−x Mg x TiO3 (SMT) (x ⩽0.30) films annealed at 750°C, all Mg ions were accommodated in the perovskite lattice and for SMT films annealed at 900°C, the solubility limit of Mg was x =0.10, above which a Mg-rich ilmenite second phase was observed. Irrespective of the higher solid solubility limit of Mg in the ST lattice for sol–gel ST films compared to equivalent ceramics, no ferroelectric or relaxor phase transition was observed, refuting previous predictions for this dopant. [Copyright &y& Elsevier]

Abstract: This paper explains the limits of processing conditions for Pb(Zr,Ti)O3 (PZT) thick films on Cu substrates. PZT thick films in the thickness range 5–20μm deposited on flexible Cu foils by electrophoretic deposition showed poorer properties when compared with PZT thick films deposited on Pt foils under identical conditions. Although the density of the sintered films and the electrical properties were improved by introducing a PbO coating on the top of the films, the dielectric and ferroelectric properties of PZT thick films on Cu were still inferior to those of films deposited on Pt. Rutherford backscattering spectrometry, X-ray diffraction and transmission electron microscopy revealed the formation of a Cu x –Pb alloy when sintering above 950°C, accompanied by Ti enrichment of the PZT and the formation of ZrO2 phases. As the sintering temperature increased, the concentration of the metallic phase increased and spread throughout the film. A new Pb–Cu alloy phase was identified. The poorer electrical properties of PZT thick films on Cu were correlated with these microstructural features. [Copyright &y& Elsevier]

Abstract: REBaCo2O6−δ (RE =Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho) phases were prepared by solid-state reaction at 1100 °C. Post-reaction heat treatments were carried out to alter the oxygen contents, which were determined by H2-reduction thermogravimetry. Three closely-related structure types were observed, with the general sequence: tetragonal to orthorhombic to tetragonal with increasing oxygen content. Rietveld refinement of combined X-ray and neutron powder diffraction data of NdBaCo2O6−δ was carried out for four values of δ. Oxygen deficiency is accommodated by partial occupancy of two sets of oxygen sites, giving a range of coordination environments for Co. Electron diffraction patterns revealed a superlattice with Cmmm symmetry, where and refer to the (pseudo) tetragonal subcell. Tweed-like ferroelastic domains were routinely observed, suggesting that compositions that appear macroscopically tetragonal by X-ray diffraction are in fact orthorhombic with . [Copyright &y& Elsevier]

Abstract: Ba2LaTi2Nb3O15 exhibits a smeared maximum of permittivity, characteristic of classic relaxor behaviour, with a peak shift from 185K at 100Hz to 300K at 1GHz. Ba2NdTi2Nb3O15 undergoes a first order ferroelectric phase transition at 389K and Ba2La0.5Nd0.5Ti2Nb3O15 exhibits both a ferroelectric phase transition at 274K and relaxor behaviour at higher temperatures. All three ceramic systems were investigated across a broad frequency (100Hz–1THz) and temperature (10–500K) range. Slowing down of the dielectric relaxation across the whole investigated temperature range from the THz and microwave regions to below 100Hz was observed on cooling in the relaxor ferroelectric Ba2LaTi2Nb3O15. The mean relaxation frequency obeys the Vogel–Fulcher law with freezing temperature of 40K. In Ba2NdTi2Nb3O15 and Ba2La0.5Nd0.5Ti2Nb3O15 the relaxations soften only in the paraelectric phase down to the 1GHz and 100MHz range, respectively. Below T c the relaxations vanish. The origin of the dielectric relaxations is discussed on the basis of structural data. [Copyright &y& Elsevier]

Abstract: The compositions Ba2MTi2X3O15: M=La, Pr, Nd, Sm, Eu, Gd, Dy, Bi; X=Nb, Ta form a new family of ferroelectric phases. With larger M cations, La, Bi, the materials exhibit relaxor behaviour with sub-ambient Tc. With decreasing M size, a sharp first order ferroelectric phase transition is observed and Tc rises to a maximum at ∼330°C for Gd. The phases are tetragonal tungsten bronzes with A-site order (BaM) and non-statistical B-site disorder (of Ti, Nb for M=La). All phases show a weak superstructure with doubled c and multiple periodicity parallel to [110] that is incommensurate for the relaxor ferroelectrics (M=La, Bi) but commensurate for the remainder. The phases exhibit complex non-stoichiometry with variable Ba:M and Ti:X ratios as well as variable oxygen content. [Copyright &y& Elsevier]

x CaTiO3–(1−x) Sr(Mg1/3Nb2/3)O3 (CTSMN) and y CaTiO3–(1−y) NdAlO3 (CTNA) were studied by Raman spectroscopy. A sharp Raman band at 825 cm−1 was observed in SrMg1/3Nb2/3O3, consistent with 1:2 long-range ordering of cations on the B-site. The intensity of this band decreased and its width increased with increasing x implying that the degree of order was reduced. A broad Raman band around 800 cm−1, absent in both pure CaTiO3 and NdAlO3, was found in CTNA solid solutions with the strongest intensity at x=0.5. The position and intensity of this band suggested that its origin was similar in nature to that observed in CTSMN. The occurrence of a band at ∼800 cm−1 in CTNA suggested a non-random distribution of Ti4+ and Al3+ on the B cation sites. [Copyright &y& Elsevier]

Room-temperature infrared reflectivities, time-domain THz transmission spectra and micro-Raman spectra of ceramics in the Ruddlesden–Popper homologous series, Srn+1TinO3n+1 (where n=1, 2, 3, 4, ∞), were studied. Increasing the number of perovskite layers (n) in the crystal system resulted in higher polarizability of the lattice and softening of the lowest frequency phonon mode, which is responsible for the observed increase in microwave permittivity, dielectric loss and temperature coefficient of resonance frequency with n. Although the infrared and Raman spectra revealed many defects in the ceramics (e.g. second phases and stacking faults), the extrapolation of experimental submillimetre dielectric data to the microwave region showed no dielectric dispersion below the phonon frequencies and prevailingly an intrinsic origin of losses in the microwave region in almost all samples (except for Sr5Ti4O13). [Copyright &y& Elsevier]

Solid solutions of the system (x)CaTiO3–(1−x)Sr(Mg1/3Nb2/3)O3 (CTSMN) were prepared by the mixed oxide route. All compositions were found to be single phase by X-ray diffraction; pellets had densities >95% of the theoretical X-ray density. Scanning electron microscopy coupled with energy dispersive X-ray analysis revealed a homogeneous distribution of cations within instrument sensitivity in all samples except for pure SMN which showed evidence of some unreacted MgO. SMN is reported as a 1:2 ordered trigonal/hexagonal complex perovskite structure in the X-ray data files but electron diffraction revealed superlattice reflections characteristic of both in-phase and anti-phase rotations of octahedra arising from further structural phase transitions on cooling. These reflections were retained throughout the solid solution range but ±1/3{hkl} ordered superlattice reflections were absent in samples where x > 0.1. In general, the microwave quality factor (Qu*fo) decreased as x increased and the temperature coefficient of resonant frequency (TCf) was approximately linearly proportional to the permittivity; at x∼0.20: TCf∼0, &epsiv;r ∼45 and Qu*fo ∼9000. [Copyright &y& Elsevier]

The hexagonal polymorph of BaTiO3 (P63/mmc) has been stablished at room temperature by partial replacement of Ti by Ga, where BaTi1-yGayO3-y/2 and 0.06≤y≤0.125 for samples prepared at 1300°C. The unit cell expands with increasing y and Rietveld Refinement of Neutron diffraction data shows that oxygen vacancies occur only in the hexagonal close packed layers between the face-sharing Ti2O9 dimers. Exaggerated grain growth (>100 μm) occurs for ceramics processed at ≥1400°C and/or for sintering periods ≥2 hours. Electrical measurements show the materials to be electrically insulating with room temperature permittivity values of ~70–80. Dense ceramics (94–97% of the theoretical X-ray density) resonate at microwave frequencies with Q.f values of ~4000–8000 at ~5.5 GHz. [Copyright &y& Elsevier]