Role of filler lanthanide ions on lattice dynamics of phosphide skutterudites RFe_4P_12 (R = La, Ce, and Pr) from first principles
arxiv(2024)
摘要
Phosphide skutterudites primarily show promise for thermoelectric
applications due to their chemical stability at high temperatures and
relatively low cost. Ion doping and band gap engineering have been used to
enhance their typically poor thermoelectric performance, opening avenues for
practical applications. Herein, we report a comparative lattice dynamics study
on the impact of filler and temperature on the structural and vibrational
properties of RFe_4P_12 (R = La, Ce, and Pr) skutterudites. Calculations
are performed within the quasi-harmonic approximation, and the results are
critically compared against experimental data and other ab initio
calculations. We found gaps between the heat-carrying acoustic and optical
modes, a-o gaps, of approximately 4, -2, and 0.01 cm^-1 for La, Ce, and Pr
compounds, respectively. These results suggest a filler-induced reduction in
the a-o gap is attributed to the softening of the optical modes instead of the
conventionally considered upward shift of acoustic modes proposed in the
rattling scenario. The distinct softening of the optical modes is
rationalized by the stiffening of chemical bonds between the filler and host
lattice.
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