High-Temperature Neutron Diffraction Study of Y4Al2O9

Theoretical prediction on mechanical and thermal properties of a promising thermal barrier material: Y4Al2O9

“…As shown in Table 1, the calculated lattice parameters are very close to the theoretical ones calculated by Zhan et al [7], but are smaller than the experimental data [39]. The smaller geometry optimized lattice constants can be understood from the following two aspects.…”

“…where parameter   is a correction parameter from the analysis of experimental results, which depends on the position of cation in the periodic The calculated lattice parameters of Y 4 Al 2 O 9 using DFT are listed in Table 1, together with the previously reported experimental data [39] for comparison. As shown in Table 1, the calculated lattice parameters are very close to the theoretical ones calculated by Zhan et al [7], but are smaller than the experimental data [39].…”

“…The Mulliken populations of Al-O bonds are higher than that of Y-O bonds, indicating higher level of covalency of Al-O bonds. Table 3, where the bond lengths used in the calculations are from the experiment data [39] , and Y(4) atoms are coordinated with seven O atoms. These structural features play an essential role in the elastic and thermal properties of this material, which will be discussed in the following sections.…”

“…The bulk modulus for polycrystalline Y 4 Al 2 O 9 is estimated to be 118 GPa, which is lower than the value (132 GPa) calculated by first-principles. The main reason for the low bulk modulus estimated from the chemical bond theory is that large experimental lattice constants from high temperature neutron diffraction [39] were used. If small lattice constants were used, the estimated bulk modulus should be close to the first-principles calculated value.…”

Preparation, mechanical, and thermal properties of a promising thermal barrier material: Y4Al2O9

“…One can see from the figure that the as-prepared YAM is phase-pure without any impurities detectable by XRD. Since the previous determined lattice parameters and atomic positions are from high-temperature neutron diffraction at 1791 K [11], which are different from the room temperature data due to thermal expansion, Rietveld refinement was performed to obtain the lattice constants, atomic positions, and intensities of YAM. The lattice constants are a = 7.3865 Å, b = 10.4750 Å, c = 11.1251 Å, and  = 108.6264.…”