Pyrochlore structure β-Bi2Sn2O7 as reversible thermochromic pigments

Pyrochlore structure of β-Bi2Sn2O7 shows continuously reversible thermochromic property from pale-yellow (25 °C) to reddish-brown (550 °C) in either heating or cooling process. Calcination for longer time (24 h versus 10 h) for the β-Bi2Sn2O7 pigments synthesized via solid state method relieves the distribution of defects and soften the Bi-O bonds in the orthorhombic Aba2 (No.41) lattice, facilitating lower bandgap and higher chromatic aberration, which indicate a crucial role of oxygen defect control for Bi-O-based thermochromic materials. This new finding is important for the design and fabrication of other charge-transfer type reversible thermochromic materials, which would definitely benefit for the next generations of smart inorganic pigments.