Electrical and Optical Properties of [001]-oriented Silver NiobateSingle Crystal

Silver niobate (i.e., AgNbO₃, AN) as a lead-free antiferroelectric material has a promising application in energy storage and photocatalysis. However, a lack of theoretical understanding due to the heterogeneity of ceramic microstructures affects its further development. In this study, high-quality [001]-oriented AN single crystal was grown with AgCl as a co-solvent. This crystal exhibited energy storage density and efficiency comparable to AN ceramic, along with superior photovoltaic performance. The [001]-oriented AN single crystal demonstrated exceptional withstand voltage characteristics, surpassing those of AN ceramic. This work could provide crucial insights into the optoelectronic performance of AN single crystals, paving a way for potential applications in high-energy storage capacitors, piezoelectric devices, and photocatalysis.

In this study, pure-phase raw materials were synthesized by a solid-state reaction method, followed by the growth of AN single crystals by a modified co-solvent method. The raw materials from Sinopharm Chemical Reagent Co., Ltd., China, were Ag₂O (99.7% purity) and Nb₂O₅ (99.5% purity), which were ground, dried, and then calcined in an oxygen atmosphere at 900℃ for 6 h to obtain pure-phase AN. The raw materials were mixed with a specific amount of AgCl (99.5% purity), and heated in double corundum crucibles in an oxygen atmosphere at 1180 ℃ for melting. The melt was then slowly cooled to 1140 ℃ for nucleation and further cooled to room temperature to obtain single crystals. Finally, the residual AgCl was removed through ammonia treatment.

The [001]-oriented AgNbO₃ (AN) single crystals exhibit higher phase transition temperatures, compared to conventional AN ceramics, due to their high crystallinity and specific orientation. These crystals also demonstrate exceptional optoelectronic properties, with a forbidden bandwidth of 2.82eV, enabling an effective UV absorption at below 440nm and stable visible light transmittance at above 470 nm. Furthermore, the [001]-oriented AN single crystal shows remarkable withstand voltage characteristics, maintaining a stability at a bias voltage of up to 190 V, significantly exceeding those of AN ceramic (i.e., ~10V). The leakage current increases linearly and symmetrically with voltage and optical power, highlighting their potential for high-voltage, high-power applications. In summary, the [001]-oriented AN single crystal offers unique advantages for photodetectors and optoelectronic devices due to their enhanced phase transition temperatures, superior optoelectronic properties, and exceptional withstand voltage characteristics. A future research can focus on further optimizing their performance and expanding their applications in optoelectronic technology.

In this study, high-quality [001]-oriented AgNbO₃ (AN) single crystals were grown with AgCl as a co-solvent. The crystals exhibited comparable energy density and conversion efficiency to the same-composition ceramics with higher phase transition temperatures due to their crystallinity and orientation. The forbidden bandwidth of 2.82 eV enabled an effective UV light absorption at below 440 nm and a good visible light transmittance at above 470 nm. The crystals demonstrated excellent withstand voltage characteristics, maintaining a stability at high bias voltage and exhibiting a linear relationship between leakage current and voltage/optical power. These results could underscore a potential of [001]-oriented AN single crystal for high-voltage, high-power optoelectronic applications.