Physical properties of La2B2O7(B Zr, Sn, Hf and Ge) pyrochlore: First-principles calculations

Abstract

Using first-principles theory and further verified by the experimental results, we have studied the electronic structure, mechanical and thermal properties of La 2 B 2 O 7 (B=Zr, Sn, Hf and Ge) pyrochlore. It is shown that the La 2 B 2 O 7 pyrochlore are charge-transfer-type insulators with the strong ionic bonding. The calculated band gap of La 2 Zr 2 O 7 , La 2 Sn 2 O 7 , La 2 Hf 2 O 7 , and La 2 Ge 2 O 7 are 4.01, 3.05, 3.13 and 2.42 eV, respectively. The elastic constants, hardness, shear modulus, bulk modulus, Young's modulus and Poisson's ratio of La 2 B 2 O 7 compounds were investigated systematically. Anisotropic elastic and thermal properties of La 2 B 2 O 7 compounds were discussed by using Zener's indexes (A Z) and universal elastic anisotropic index (A U). The sound velocities along [100], [110] and [111] directions were calculated for each La 2 B 2 O 7 compounds. Both Clark's model and Cahill's model were used to evaluate the minimum thermal conductivity of all compounds. According to the Clark's model, when the temperature is much higher than Debye temperature, the minimum thermal conductivity of La

Impact of isovalent and aliovalent substitution on the mechanical and thermal properties of Gd2Zr2O7

“…As compared with the experimental measurement, our calculated elastic moduli for Gd 2 Zr 2 O 7 and Sm 2 Zr 2 O 7 are overestimated slightly. This may be resulted from the employed LDA method, which generally underestimates the lattice constant whereas overestimates the mechanical modulus 41 . Besides, the defects and impurities in the sample experimentally may also lead to the underestimated values of the B and G 41 .…”

“…This may be resulted from the employed LDA method, which generally underestimates the lattice constant whereas overestimates the mechanical modulus 41 . Besides, the defects and impurities in the sample experimentally may also lead to the underestimated values of the B and G 41 . Variation of the elastic moduli for Sm y Gd 2-y Zr 2 O 7 and Gd 2 Sm y Zr 2-y O 7 with the Sm content is illustrated in Fig.…”

“…Here, h is the Planck’s constant, k B is the Boltzmann’s constant, n is the number of atoms in molecular, N A is the Avogadro’s constant, ρ is the density, M is the molecular mass and v m is the sound wave velocity. The v m can be deduced by , where is the longitudinal sound velocity and is the transverse sound velocity 41 . As one can see from Table 3, Sm substitution for Gd-site has slight effects on the Debye temperature of Gd 2 Zr 2 O 7 and all the compositions have very similar results.…”

First-principles calculation and experimental investigation of lattice dynamics in the rare-earth pyrochloresR2Ti2O7(R=Ruminy1, Valdez2, Wehinger3 et al. 2016Phys. Rev. B336480View full textAdd to dashboardCite

“…For the former, first-principles calculations were used in the study of defect formation in the pyrochlore structure, while for the latter thermodynamic properties were simulated using both the molecular dynamics method [11] and ab initio calculations [13][14][15]. For both applications, it was found that pyrochlore zirconates are generally favorable over titanates, hence more theoretical investigations on the lattice dynamics of zirconates have been carried out.…”

INFLUENCE OF SYNTHESIS PROCESS ON THE COLOUR PROPERTIES OF MIXED OXIDE PIGMENT Bi1.5Zn0.5Ce₂O₇

“…1000°C was chosen. In case of X-ray diffraction analysis, the pyrochlore compounds occur as defective fluorite and can be exchanged for cerium oxide because the pyrochlore structure is closely related to the fluorite structure and can be thought of as a cation-ordered anion deficient fluorite lattice, in which the cations form a face-centered cubic array [17]. In the database for the evaluation of the composition studied compounds samples were often compared with cubic CeO 2 (lattice parameter a = 0.5411 nm) [18].…”