High photoelectronic response with a broad spectral range in photoelectric materials is of great importance for photovoltaic and photocatalytic applications. However, the existing photoelectric materials, such as TiO 2 and α-Fe 2 O 3 , exhibit only high photoelectronic response or only broad spectral response because of the wide band gap limitation of light absorbance or low photogenerated charge separation efficiency. Here, we report NaBiO 3 •2H 2 O annealed at a given temperature to form NaBiO 3 • 2H 2 O/NaBiO 3 •xH 2 O heterostructures, which efficiently drives the photogenerated charge separation in a broad spectral range. The best performance of the wide photoelectronic response and high surface photovoltage was obtained in the sample annealed at 130 °C. The high surface photovoltage with a wide spectral range is attributed to the band gap engineering of NaBiO 3 •2H 2 O/NaBiO 3 •xH 2 O heterostructures for efficient photogenerated charge separation. These findings regarding the use of optimized NaBiO 3 • 2H 2 O/NaBiO 3 •xH 2 O heterostructures suggest that fine-tuning the heterostructure of the photoelectric materials is an effective approach for improving the photoelectrical performance in optoelectronic applications.

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Tailoring the thermal expansion coefficient of negative thermal expansion (NTE) materials to achieve near-zero thermal expansion has attracted great attention recently. Here, LiFe diatoms are adopted to substitute Cu in Cu 2 P 2 O 7 oxide to design Li−O−P and Fe−O−P linkages, with the stronger bond strength of Li−O and Fe−O compared to Cu−O and hence lowering the bond strength of P−O. With increasing the diatomic LiFe in (LiFe) 0.5x Cu 2−x P 2 O 7 , new Raman bands corresponding to LiFeP 2 O 7 appear and the NTE coefficient decreases gradually to near-zero thermal expansion at x = 1 (α v = −0.90 × 10 −6 °C−1 , −100 to 55 °C). Comparing (LiFe) 0.5 CuP 2 O 7 with Cu 2 P 2 O 7 and LiFeP 2 O 7 , the average bond length of P−O increases while the bond angle of P−O−P decreases, and this is verified by some weakened vibrational energies of terminal PO 3 and P−O−P, resulting in the obvious red shift of Raman bands. Ceramic (LiFe) 0.5 CuP 2 O 7 presents a lower difference in grain size and a higher relative density than Cu 2 P 2 O 7 and LiFeP 2 O 7 .

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