RECrO₃ as High-Contrast Thermochromic Memory Pigments: Enabled by Hydrothermal Distortions and Magnetic Tuning (RE = Eu, Tb, Y)

Inorganic crystals synthesized via different methods with the "same" composition often exhibit distinct properties, a phenomenon frequently overlooked or misinterpreted. In this work, we demonstrate the peculiar magnetic properties and thermochromic memory behavior of three perovskite-structure rare-earth chromites (RECrO₃, RE = Eu, Tb, and Y) synthesized by a mineralizer-assisted hydrothermal method at 225 °C. The crystals feature an elongated <i>b</i>-axis and greater distortion of the CrO₆ octahedral subunits. Crystal shapes are sensitive to the composition, mineralizer concentration, and reaction temperature. Raman and infrared peaks show a RE³⁺-dependent behavior. All samples are canted-antiferromagnetic with significantly lower Néel temperatures than the samples synthesized via other methods. Three notable magnetic transition points are shown in TbCrO₃, which have never been found in other samples. Temperature and magnetic field dependent magnetization curves of EuCrO₃ samples show crystal shape dependent magnetic behaviors. All of the samples show continuously irreversible thermochromic properties from 100 to 500 °C with color changes from yellowish green to reddish brown with the highest chromaticity aberration of Δ<i>E</i> = 51.47 in TbCrO₃. This work indicates that the materials synthesized via the mineralizer-assisted hydrothermal crystallization method facilitate versatile tunability of the structure and physical properties with promising thermal recording applications.