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XRD and SEM studies of the formation of Bi2TeO6 confirmed that the Bi2TeO6 compound forms in an oxygen atmosphere and also during prolonged calcination in air. At elevated temperatures the compound decomposes with the degree of the decomposition being dependent on the oxygen partial pressure. The decomposition products were identified as Bi6Te2O15 and the high-temperature phase 2Bi2O3·3TeO2+x. The sublimation of TeO2 was proved not to be the main reason for the appearance of the Bi6Te2O15 phase during the decomposition of Bi2TeO6. [Copyright &y& Elsevier]

Abstract: We have investigated the Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 (NBT–KBT) system, with its complex perovskite structure, as a promising material for piezoelectric applications. The NBT–KBT samples were synthesized using a solid-state reaction method and characterized with XRD and SEM. Room-temperature XRD showed a gradual change in the crystal structure from tetragonal in the KBT to rhombohedral in the NBT, with the presence of an intermediate morphotropic region in the samples with a compositional fraction x between 0.17 and 0.25. The fitted perovskite lattice parameters confirmed an increase in the size of the crystal lattice from NBT towards KBT, which coincides with an increase in the ionic radii. Electrical measurements on the samples showed that the maximum values of the dielectric constant, the remanent polarization and the piezoelectric coefficient are reached at the morphotropic phase boundary (MPB) (ɛ =1140 at 1MHz; P r =40μC/cm2; d 33 =134pC/N). [Copyright &y& Elsevier]

Abstract: The high-temperature behaviour of K0.5Bi0.5TiO3, prepared using a conventional solid-state reaction method, was investigated using X-ray powder diffraction, scanning electron microscopy, wavelength-dispersive X-ray spectroscopy and Knudsen effusion combined with mass spectrometry. The results revealed the formation of an off-stoichiometric matrix phase with an excess of bismuth and a deficit of potassium compared to the stoichiometric K0.5Bi0.5TiO3 during the solid-state reaction. During the thermal treatment potassium and bismuth vapours were detected over the solid sample and related to the thermal decomposition of the matrix phase. The losses of the potassium and bismuth components shifted the nominal composition to a three-phase region, and as a result, K2Ti6O13 and a new Bi-rich ternary phase were formed in the system, the latter being formed after prolonged sintering. Differential thermal analyses and heating-microscope analyses showed a narrow sintering-temperature range limited by the melting of the sample above 1040°C. [Copyright &y& Elsevier]

Abstract: Phase relations in the Bi2O3–TiO2–WO3 ternary system were evaluated for different compositions calcined in air at 850°C by means of XRD techniques. A solid solution area was observed for Bi4Ti3O12 compositions with a small amount of WO3. The experimental results suggest the existence of a new phase with a nominal composition close to Bi3Ti2.5W0.5O11. This phase allows the definition of four triangles of compatibility at 850°C in the ternary system. The new phase was characterized by XRD, SEM and EDS. [Copyright &y& Elsevier]

Abstract: Microwave dielectric properties of fluorite-like (1− x)Bi2O3–xNb2O5 solid solutions with various x between 0.1 and 0.26 are compared with complex dielectric response in THz and infrared frequency range between 0.1 and 100THz, which allows the estimation of intrinsic and extrinsic dielectric losses. The best quality sample with the most attractive properties was found for x =0.26 composition with the permittivity of 86, Qf =1000GHz and τ f =120ppm/K. Our ceramic system exhibits two different crystal structures depending on Nb2O5 concentration and it is shown how the infrared reflectivity spectra can help to distinguish the structures. τ f can be reduced to zero by mixing of Type II and Type III structures. [Copyright &y& Elsevier]