Papers by Keyword: La₂Zr₂O₇

Abstract: In order to achieve better understanding of the effect of dopant (Sc, Y, Yb, Hf and Ce) on elastic stiffness and thermal properties of La2Zr2O7. The related calculations were performed using the first principles methods. The predicted elastic constants indicate that La2Zr2O7 and oxidations-La2Zr2O7 (oxidations refer to Sc2O3, Y2O3, Yb2O3, HfO2 and CeO2) are mechanically stable structures. And then the numerical estimates of bulk modulus, shear modulus, Young’s modulus were performed using the calculated elastic constants. After these mechanical properties are obtained, sound velocity, Debye temperature and theoretical minimum thermal conductivity of La2Zr2O7 and oxidations-La2Zr2O7 are calculated and analyzed in detail. The available experimental results and our calculations are basically satisfactory. The calculated results indicate that Young’s modulus, mean sound velocity, Debye temperature and minimum thermal conductivity of La2Zr2O7 can be decreased by dopants. CeO2 has extraordinary ability to decrease thermal conductivity in these dopant oxidations.

Abstract: Thermal barrier coatings (TBCs) system has been the subject of vigorous research over the past decade, driven by the demands for enhanced reliability and substantially higher operating temperature envisaged for the next generations of gas turbine engines. As a novel structure system, the double ceramic layer design is a promising TBCs structure system , especially its long thermal cycling lifetime compared with the single ceramic layer. This paper mainly reviewed of development situation and the existing problems of several mainly double ceramic layer thermal barrier systems, including M-YSZ/YSZ, A₂B₂O₇/YSZ, LTA/YSZ, LnMA/YSZ, ABO₃/YSZ and so on. Many challenges remain but healthy and growing collaborations between the science and technology communities bode well for future progress in this area.

Abstract: La₂Zr₂O₇ as the thermal barrier coating material draws more and more attention because of its greater thermal physical properties than YSZ, while its further application is restricted by its poor mechanical properties. In this paper, certain ZrO₂ is added into the La₂Zr₂O₇ ceramics in order to improve its mechanical properties. La₂Zr₂O₇ ceramic superfine powder was synthesized by the co-precipitation method and samples of La₂Zr₂O₇-xZrO₂(x=0, 10%, 20%, 30%)were prepared by pressureless sintering process. The microstructure and properties of the samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), three-point bend tests, SENB, laser impulse thermal conductivity instrument and high-temperature expansion instrument. Owing to the partial solid solubility in the La₂Zr₂O₇-xZrO₂ ceramics, ZrO₂ exists in the form of m-ZrO₂ and t-ZrO₂. With the addition of ZrO₂, the mechanical properties of La₂Zr₂O₇-xZrO₂ ceramics first increase, then decrease. When the addition amount of ZrO₂ reaches 20%, the fracture toughness comes to the greatest value 2.41 MPa·m^1/2. When the addition amount of ZrO₂ reaches 10%, the bending strength comes to the greatest value 202.4 MPa. The thermal conductivity of the La₂Zr₂O₇-xZrO₂ ceramics is lower than YSZ. The thermal conductivity of the La₂Zr₂O₇-xZrO₂ ceramic decrease at 1400 °C as the addition amount of ZrO₂ increases, resulting from the higher intrinsic thermal conductivity of ZrO₂ than that of La₂Zr₂O₇. The thermal expansion coefficient of the La₂Zr₂O₇-xZrO₂ ceramics decreases slowly after about 350 °C and decrease rapidly at about 1000 °C, and then increase rapidly due to the transformation of m-ZrO₂ to t-ZrO₂.

Abstract: Transparent La2Zr2O7 with cubic pyrochlore structure was first fabricated by reactive spark plasma sintering using commercially available La2O3 and ZrO2 powders. Single phase of pyrochlore La2Zr2O7 was obtained at a sintering temperature of 1673 K and sintering pressure at 100 MPa for 2.7 ks. The La2Zr2O7 sintered body had a uniform grain size of 1.5 m and exhibited 68% transmittance in the wavelength range of 4–6 m.

Abstract: Materials with A2B2O7 (pyrochlore) structure have received a significant attention for their applications as new protonic conductors and materials used in electronic devices. One of the unique synthesis routes for La2Zr2O7 (pyrochlore) powders is the glycine-nitrate combustion method, which shows superior properties of the synthesized powder by using glycine as a complexing agent. The Sr doped La2Zr2O7 powders in pure pyrochlore structure were produced using this approach. Selected characteristics of the synthesized powders, such as crystal structure, lattice parameters, crystallite size, the vibrational properties, the morphology of the particles, along with the specific surface area and particle size have been investigated. The dependence of some properties on annealing temperatures of the powders has been studied.