Theoretical Predictions on Elastic Stiffness and Intrinsic Thermal Conductivities of Yttrium Silicates

Abstract

Yttrium silicates are promising candidates for environmental and thermal barrier coatings owing to their excellent high-temperature performances. Previous works have experimentally attested to their low thermal conductivity, nevertheless, the experimental data were significantly affected by measurement inaccuracy and the existence of defects such as point defects, dislocations, grain boundaries, and pores in measured samples. In this study, the temperature dependences of intrinsic lattice thermal conductivities of c-Y 2 Si 2 O 7 and Y 2 SiO 5 are predicted based on the first-principles calculations of crystal structure, elastic moduli, Debye temperature, and Gr€ uneisen constant. Both silicates display very low thermal conductivities over the range of 300-2000 K; and in addition, Y 2 SiO 5 exhibits relatively lower thermal conductivity than c-Y 2 Si 2 O 7 . We also show certain discrepancies between experimental and theoretical thermal conductivities, and it strengthens the important role of theoretical prediction of intrinsic lattice thermal conductivities of promising materials.

Low thermal conductivity of Lu4Si2O7N2: Theoretical and experimental studies

“…6, together with the theoretical minimum thermal conductivities and experimental results for comparison. We can see that the thermal conductivity of Lu 4 Si 2 O 7 N 2 follows κ = 852/T (in W m −1 K −1 ) and approaches to the minimum value at temperature about 960 K. When comparing with the experimental ones, it can be seen that the experimental value is higher than the theoretical predicted ones at temperatures over 576 K. Similar phenomena have been noticed and explained in recent work in ␥-Y 2 Si 2 O 7 and Y 2 SiO 5 [45]. It is also shown that theoretical thermal conductivity is higher than its experimental value at lower temperature, and the gap is gradually narrowed until vanished.…”

Approximate lattice thermal conductivity of MAX phases at high temperature

“…This illustrates that in MAX phases, the minimum lattice thermal conductivity should be at relative high temperature close to 2000 K. It also demonstrates the results from Clarke's formula to be close to that predicted by Slack's equation at high temperature despite their different derivations and approximations. We still could not explain such a wide variations in κ min in MAX phases but the data could provide an overall picture of their minimal lattice thermal conductivity with potential implications on possible applications as TBC materials at high temperature [20]. The main conclusion is that generally speaking, MAX carbides have their minimal lattice thermal conductivity larger than the nitrides.…”

“…Hence, θ D calculated from elastic parameters should be the same as those obtained from the specific heat measurements at low temperature. One of the accepted practice is to obtain θ D from average phonon velocity v m by using the following expression [20].…”

Accurate Exploration of the Intrinsic Lattice Thermal Conductivity of Si2N2O by Combined Theoretical and Experimental Investigations

“…Based on Slack model, it is convenient to calculate thermal conductivity from several material parameters that can be deduced by DFT calculation. Recently, Feng, Luo, and Tian successfully combined density functional theory with Slack model to predict the temperature‐dependent lattice thermal conductivities of complex rare‐earth monazite‐type phosphates and silicates.…”

“…A (γ) [W·mol·kg −1 ·m −2 ·K −3 ] is calculated by:…”