A systematic first-principles investigation of the structural, electronic, optical, thermodynamic and transport properties of lead-free pyrochlore oxides Q2Sb2O7 (Q= Be, Ca, Sr) for low-Cost energy applications.

A systematic study has been performed on structural, optical and thermophysical properties of newly designed pyrochlore oxides Q 2 Sb 2 O 7 (Q = Be, Ca, Sr) employing FP-LAPW based first-principles calculations. The GGA approach was used to treat exchange and correlation potentials. The investigated E-V plots reveals that Sr 2 Sb 2 O 7 is the most stable structure compared to Be 2 Sb 2 O 7 /Ca 2 Sb 2 O 7. A direct energy bandgap of 0.29 eV is evident from band structure plot of Be 2 Sb 2 O 7 , however, Ca 2 Sb 2 O 7 /Sr 2 Sb 2 O 7 possess indirect energy bandgaps of magnitude 1.47/1.467 eV. The studied materials show maximum absorption of incoming photons in near UV region as shown in ε 2 (ω) plots, however, considerable absorption in visible region is also present. Ca 2 Sb 2 O 7 /Sr 2 Sb 2 O 7 are effective optical material with a n (ω) value between 1.0 and 2.0. Optical properties of pyrochlore oxides reveal that these materials are potential candidates for shielding materials in upper UV region. A photon reflection of up to 60% is evident from the R (ω) in UV region, however, in IR and visible regions, the reflectance is negligible. Based on calculated values of Seebeck coefficient (S), we can state that Be 2 Sb 2 O 7 is n-type semiconductor whereas Ca 2 Sb 2 O 7 /Sr 2 Sb 2 O 7 are p-type semiconductors. The most effective thermoelectric material among Q 2 Sb 2 O 7 (Q = Be, Ca, Sr) is Ca 2 Sb 2 O 7 as its ZT value is highest (∼1.05) in the entire temperature range. Thermodynamic properties of Q 2 Sb 2 O 7 (Q = Be, Ca, Sr) are also evaluated to check dynamical stability and appropriateness of these materials in thermal applications. The investigated outcomes show that these pyrochlore oxides are potential candidates for thermoelectric and optoelectronic device applications. • Ground state properties of pyrochlore oxides Q 2 Sb 2 O 7 (Q = Be, Ca, Sr) are investigated using ab-initio. • Q 2 Sb 2 O 7 (Q = Be, Ca, Sr) are narrow band semiconductors. • Be 2 Sb 2 O 7 is n-type semiconductor, however, Ca 2 Sb 2 O 7 /Sr 2 Sb 2 O 7 are p-type semiconductors. • Optical spectra show major absorption peaks for these pyrochlore oxides occur in visible region. [ABSTRACT FROM AUTHOR]