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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 phase evolution of Er3+ doped oxy-fluoride glass ceramics as a function of temperature has been investigated. Differential thermal analysis showed two successive crystallization exotherms. The first, around 480 °C, was characterized using X-ray diffractometry (XRD) and transmission electron microscopy (TEM) and was related to the formation of a nanocrystalline PbF2 phase, hosting most of the rare earth ions. The second crystallization event was studied using XRD, scanning electron microscopy and TEM. It was established that nucleation occurred at the surface, accompanied by Pb loss. Cd-silicate phase together with Zn-fluoride and an Al–Zn oxide phases were present according to energy dispersive X-ray analysis. Not all peaks in XRD traces could be assigned to known compounds. However, several reflections matched well to either CdSiO3 (JCPDS [35-810]) or ZnF2 (JCPDS [71-1971]). [Copyright &y& Elsevier]

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]