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In Ca doped CePO 4 monazite (viz., Ce 0.8 Ca 0.2 PO 4 ) cerium exhibits mixed valence state (+3 and +4) and therefore can accommodate cations of any valence (by converting Ce 3+ to Ce 4+ or vice versa) subject to the size and other restrictions. A simulated waste form prepared based on the versatile monazite phase, Ce 0.8 Ca 0.2 PO 4 , showed higher leaching for Cs and Mo indicating that these elements do not enter the monazite lattice. Iron phosphate glass (IPG) is an alternate glass waste form considered for HLW immobilization. A glass–ceramic composite of crystalline monazite and IPG could have synergistic effects and can improve the leaching resistance. The preparation and characterization of a versatile monazite–IPG glass–ceramic waste form with 20 wt.% simulated HLW oxides and its leaching behavior are reported in this paper. The monazite–IPG glass–ceramic simulated waste form is found to have excellent chemical durability. [ABSTRACT FROM AUTHOR]

Abstract: Lanthanum chromite (LaCrO3) is currently the most widely studied material as interconnector layers for solid oxide fuel cells (SOFC). The complexity of microstructures and geometries of SOFC devices, which are usually built-up by lamination of the different constitutive layers, make it necessary a precise control of processing parameters to achieve the desired combination of properties. Much effort has been devoted to the processing of electrodes and electrolytes but the other layers, such as that of interconnecting material, have received scarce attention. This work deals with the preparation and optimisation of the rheological behaviour of concentrated suspensions of Sr- and Co-doped LaCrO3 and the subsequent tape casting to produce homogeneous thin sheets to be used in the SOFC stack. The starting powder was produced by combustion synthesis from the corresponding nitrates and urea as a fuel, and had a final composition of La0.80Sr0.20Cr0.92Co0.08O3. These powders were dispersed in ethanol with commercial copolymers (Hypermer, KD6) to solids loading of up to 58wt%. The binding system (BS) consisted of a mixture of a binder, polyvinyl butyral-co-vinyl alcohol-co-vinyl acetate (PVA-PVAc), and two plasticizers, polyethyleneglycol (PEG400) and benzylbutylphthalate (BBP). The effect of the binding system content and the binder-to-plasticizer ratio on the tape casting performance and the characteristics of the green and the sintered tapes, were studied, as well as the influence of the casting parameters (casting speed and blades height). [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of lanthanum silicon nitride (LaSi3N5) by direct nitridation of LaSi/Si/Si3N4 powder mixture at 1400°C is described. Stepwise heat treatment schedule was adopted for the synthesis of LaSi3N5 powder, on the basis of TG–DTA measurements. Except temperature and nitrogen pressure also the ratio of constituents LaSi/Si/Si3N4 has an influence on the exothermicity of the reaction and consequently on the final phase composition of the product. Silicon particle size d ≤1μm is preferable to decrease the time of nitridation. On the other hand, the reaction system must be diluted with Si3N4 to avoid the overheating of powder mix and melting of silicon. When starting from binary LaSi/Si3N4 powder mixture, additional nitridation at higher temperature (1550°C) was necessary to obtain single phase LaSi3N5 powder. The oxygen content of as-synthesized powders was in the range 1.0–1.2wt%. The lattice parameters and diffraction pattern of LaSi3N5 have been calculated and compared with experimental data. The infrared spectra of LaSi3N5 have been measured and partly described. [Copyright &y& Elsevier]

Abstract: Effect of water content in starting powder mixture of La2O3 and Mn3O4 on mechanochemical reaction of lanthanum manganite (LaMnO3) fine powder was investigated. The water content was controlled to be <0.5, 2 and 8% mass fraction in the powder mixture. An attrition-type milling apparatus was employed. This mechanochemical method has several advantages including the use of low cost raw materials, simplicity of the process and the ability to obtain fine powder. When the water content was 2% mass fraction, the single phase LaMnO3 fine powder was obtained after milling only for 30min. On the other hand, the reaction was not completed on the drier condition (<0.5% mass fraction) and the wetter condition (8% mass fraction). For the powder mixture with the water content of 2% mass fraction, the increase of specific surface area (SSA) with structural defects (forming an activated matrix) occurred in the early stage of the milling, and then solid-state reaction proceeded in the activated matrix, which led to the synthesis of crystalline LaMnO3 phase. The SSA did not change drastically with increasing milling time for the drier powder mixture. The SSA rather decreased for the wetter powder mixture. The results indicated that the water content in starting materials influenced significantly their grinding behavior and thereby the reaction rate for LaMnO3 formation. [Copyright &y& Elsevier]

Abstract: The isovalent Ba2+ modified lead lanthanum strontium zirconium niobium titanate (PLSZNT) solid solutions were prepared by solid-state reaction method with the compositional formula [Pb1−x−w−y La x Sr w Ba y ][(Zr z Ti1−z )(1−(x/4)−(5/4)k)Nb k ]O3 where Ba content, y, was varied from 0, 0.5, 1 and 1.5mol%. X-ray diffraction (XRD) studies revealed that all the samples have ferroelectric tetragonal structure (FETET). The presence of multiple ions at Pb-site enhanced grain growth and further addition of Ba concentration resulted in restrained grain growth. Dielectric studies suggested that the ɛ RT increased up to 1mol% Ba while T c has shown a continuous decreasing trend throughout the series. The piezoelectric parameters as a function of grain growth were characterized. The optimum piezoelectric charge coefficient (d 33 =538pC/N) and piezoelectric planar coupling coefficient (k p =0.521) was found to be in 1mol% Ba modified PLSZNT ceramic, respectively, and this composition may be suitable for possible sensor and actuator applications. [Copyright &y& Elsevier]

Abstract: Materials with graded composition can be obtained by a sedimentation process during which particles of a powder mixture within a suspension fall by gravity upon a substrate. This process has been used to fabricate bulk SOFC cathodes by sedimentation of lanthanum strontium manganate (LSM) and yttria stabilised zirconia (YSZ) powder mixture upon a dense YSZ substrate and subsequent firing. A numerical simulation of sedimentation based on Stokes’ law has been developed to control material and process parameters. Two cathodes with different composition gradients have been obtained by changing the initial conditions of the sedimentation. Their compositions estimated by electron dispersive spectrometry (EDS) have been found to be in reasonably good agreement with the prediction of the numerical model. [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]