Herein, the sintering behavior and dielectric properties of Ta 5+ -doped Li 3 Mg 4 NbO 8 ceramics were investigated by solid-phase reactions in combination with first-principles calculations. In particular, Li 3 Mg 4 Nb 0.96 Ta 0.04 O 8 illustrates the best dielectric properties after sintering at 1,175 °C with ε r = 13.71 ± 0.20, Q × f = (132,112 ± 2,391) GHz (increased by 25%) and τ f = (25.07 ± 1.36) × 10 −6 °C −1 . The non-intrinsic factors reflect that a small amount of Ta 5+ doping produces a secondary phase, increased densification, and grain size, all of which optimize the dielectric properties. The dominant intrinsic factors indicate that the increase in bond ionicity, the greater polarization of Ta 5+ , and the blueshift of the Raman characteristic peak all lead to an increase in ε r . The increase in lattice energy and the decrease in the damping behavior of the Nb/Ta-O bond vibrations lead to an increase in Q × f . The weakening of the Nb/TaO 6 octahedral distortion leads to an optimization of τ f . The modified Li 3 Mg 4 Nb 0.96 Ta 0.04 O 8 ceramics have promising applications in microwave communications.
Molybdenum oxide (MoO 3− x , x < 3) has been successfully used as an efficient hole-selective contact material for crystalline silicon heterojunction solar cells. The carrier transport capability strongly depends on its work function, that is, oxygen vacancies; however, there are lack of effective methods to modulate the multiple oxidation states. Herein, the oxidation states of solution-processed MoO 3− x by doping Nb 5+ to improve its hole-selective contact performance with silicon are tuned. With the optimum doping concentration of 5%, both the reduced Mo 5+ and oxygen vacancies increase, resulting in a decrease in the contact resistivity between the MoO 3− x film and p -type silicon from 161.1 to 62.9 mΩ·cm 2 and an increase of the effective carrier lifetime from 165.4 to 391.0 μs simultaneously. Similarly, the doping of Ta 5+ or V 5+ in MoO 3− x improves the passivated contact performance with silicon, while the former increases the concentration of oxygen vacancies and the latter reduces it. The solar cell with the structure of Ag/MoO 3− x :Nb/ p -Si exhibits a conversion efficiency of 18.37%, which is the highest so far reported for the solution-processed MoO 3− x /silicon heterojunction. This work demonstrates a feasible strategy of tuning hole selectivity in MoO 3− x by doping for high-efficiency solar cells and other optoelectronic device applications.
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