Dual thermochromic behavior of bismuth-doped neodymium molybdate: excellent cycling stability and color changes

Abstract

A novel inorganic thermochromic material, bismuth-doped neodymium molybdate (Nd_2−xBi_xMoO₆), was synthesized using a solid-state reaction method. The structural and thermochromic properties of the synthesized material were systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible-near-infrared diffuse reflectance spectroscopy (UV-Vis-NIR), CIE chromaticity coordinates, in situ Raman spectroscopy, and in situ XRD. The results demonstrate that as the Bi³⁺ doping concentration increases, the material's absorption edge red-shifts, and its color transitions from blue to purplish-grey. Within the temperature range of 30–300 °C, all samples display two thermochromic behaviors: an irreversible color change upon initial heating, followed by a reversible color change during subsequent heating–cooling cycles. After 100 cycles, the thermochromic performance remains stable. In situ XRD and Raman analyses indicate that the thermochromic behavior may be attributed to lattice expansion and reconfiguration of the electronic structure. This study provides a theoretical insight into the development of high-stability inorganic thermochromic materials and enriches the thermochromic material system.