Ferroelectricity and piezoelectricity in CsBiNb2O7 are demonstrated for the first time.

Ferroelectrics coupled with solar energy conversion are receiving intensive research interest. However, most ferroelectrics with a large remnant polarization can only harvest ultraviolet light in the solar spectrum. Herein, high-quality silver niobate (AgNbO 3 ) ceramics prepared by spark plasma sintering is reported with a bandgap of ≈2.75 eV and a long tail absorption until 800 nm, leading to outstanding photoelectric properties featured by the visiblelight response over 550 nm. Instantaneous photoresponse measurement using a 355 nm nanosecond pulse laser shows a fast response speed in nanoseconds. Moreover, the ceramic exhibits an intriguing photovoltaic effect under either electric poling or mechanical polishing. Both approaches have switchable characteristics and produce a stable photovoltage as well as photocurrent, while temperature dependence behavior reveals distinctions between ferroelectric polarization and ferroelastic strains in determining the photovoltaic properties. Piezoelectric force microscopy characterization further confirms distinctions between the underlying mechanisms. The electric poling induced photovoltaic effect stems from the aligned polarization involving the ferroelectric component, whereas the mechanical polishing induced photovoltaic effect is associated with the flexoelectricity induced by strain gradients. These results not only show AgNbO 3 to be a promising material for photoelectric application but also deepen the understanding of the mechanism underlying ferroelectric photovoltaics.

This work revealed that the solid solution compounds of Sr 2−x Ba x Nb 2 O 7 are promising lead-free materials for high-temperature piezoelectric sensor application. These compounds were confirmed as ferroelectric materials with high Curie points (> 900°C) by their piezoelectric activity after poling, ferroelectric domain switching in their P-E hysteresis loops and thermal depoling behavior. The effect of Ba substitution on the structure and properties of Sr 2−x Ba x Nb 2 O 7 (x < 1.0) was investigated. The solid solution limit of Sr 2−x Ba x Nb 2 O 7 was determined by XRD as x < 0.6. The a-, b-, c-axes, and cell volume increase with Ba addition. The textured ceramics of Sr 2−x Ba x Nb 2 O 7 were prepared for the first time. The highest d 33 was measured as 3.6 ± 0.1 pC/N for Sr 1.8 Ba 0.2 Nb 2 O 7 .

0.3 thermoelectric (TE) alloys containing a small amount (vol.% £5) of SiC nanoparticles were fabricated by mechanical alloying and spark plasma sintering. It was revealed that the effects of SiC addition on TE properties can be different between p-type and n-type Bi 2 Te 3 -based alloys. SiC addition slightly increased the power factor of the p-type materials by decreasing both the electrical resistivity (q) and Seebeck coefficient (a), but decreased the power factor of n-type materials by increasing both q and a. Regardless of the conductivity type, the thermal conductivity was reduced by dispersing SiC nanoparticles in the Bi 2 Te 3 -based alloy matrix. As a result, a small amount (0.1 vol.%) of SiC addition increased the maximum dimensionless figure of merit (ZT max ) of the p-type Bi 0.5 Sb 1.5 Te 3 alloys from 0.88 for the SiC-free sample to 0.97 at 323 K, though no improvement in TE performance was obtained in the case of n-type Bi 2 Te 2.7 Se 0.3 alloys. Importantly, the SiC-dispersed alloys showed better mechanical properties, which can improve material machinability and device reliability.