Design,Synthesis And Properties Of ZnGa₂O₄/ZnAl₂O₄ Spinel-Based Thermochromic Materials

With the continuous development of modern technology and economy,intelligence has become a major trend of social progress,and the design and application of intelligent materials are important parts of the realization of intelligence.Thermochromic materials,as intelligent response materials with unique color changes,have broad application prospects in aerospace,military,intelligent windows,architectural coatings,food packaging,anti-counterfeiting,temperature sensors and other fields.In recent years,thermochromic materials reported are mainly organic compounds,but because they are limited to low temperature environment,the application scope is narrow,and have side effects on organisms.In contrast,inorganic thermochromic materials have good temperature resistance,light resistance,acid and alkali corrosion resistance and low cost,so they are the ideal choices of thermochromic materials.However,there are relatively few kinds of inorganic thermochromic materials at present.Therefore,it is very important to develop new inorganic thermochromic materials which are environmentally friendly and can be applied in a wide temperature range.Spinel oxide（AB₂O₄）has attracted much attention because of its wide distribution of elements,high thermal stability and strong chemical stability.Due to its own structural characteristics,the optical properties of spinel oxide can be changed by controlled doping at the A/B sites and adjusting the crystal field strength.In this paper,based on aluminum-gallium spinel oxide as host materials,the crystal field strength are regulated by different types of host materials,the types and contents of doping transition metal elements control the base color of smart pigments at room temperature,and study the structure activity relationship between material structure and thermochromic properties,so as to design and synthesis inorganic thermochromic materials with novel properties,stable structure,sensitive and reversible color change.The main research contents are as follows:1.ZnGa₂O₄ and ZnAl₂O₄ were used as the host materials,and the crystal field strength in the host materials were regulated by changing the ions at site B,and the same amounts of chromophore Cr³⁺were introduced into the main lattice.ZnGa_2-xCr_xO₄and ZnAl_2-xCr_xO₄（x=0,0.3,0.7,1.1,1.5,1.7）series of solid solutions were successfully synthesized and their structures and thermochromic properties were characterized.All the Cr³⁺doped samples showed reversible thermochromism in the temperature range of 20°C to 500°C,among which the ZnGa_2-xCr_xO₄ series samples showed better thermochromic property.The relationships between the thermochromic behaviors and the structure of the materials were monitored by in-situ X-ray and in-situ UV-Vis-NIR absorption spectroscopy characterization techniques to monitor and systematically studied the discoloration mechanism of materials.The differences of chromic properties of Cr³⁺in two host materials with different crystal field strength were analyzed by Tanabe-Sugano level diagrams of d³ electron configuration.2.ZnGa₂O₄ was used as the host material,and the transition metal element Mn/Fe/Co doped ZnGa₂O₄ multi-color thermochromic materials were successfully designed and synthesized by element doping and changing the doping ratios to control the color properties of the materials,and their structures and properties were characterized.All the samples showed reversible thermochromism in the temperature range of 20°C to 500°C.Meanwhile,we combined in-situ UV-Vis-NIR absorption spectroscopy analysis,and found that the absorption spectrum of the material moved with the increase of temperature,which further confirmed the phenomenon of sample color change during the heating process.In this paper,the innovation researches on inorganic solid thermochromic materials are carried out from the perspectives of regulating the crystal field and the types and contents of doping transition metal elements,which enrich the color selection of inorganic thermochromic materials and provide new perspectives for the preparation of intelligent solid materials with excellent performance.