The Negative Thermal Expansion Property of NdMnO₃ Based on Pores Effect and Phase Transition

A novel negative thermal expansion (NTE) material NdMnO₃ was synthesized by solid-state method at 1 523 K. The crystal structure, phase transition, pores effect and negative expansion properties of NdMnO₃ were investigated by variable temperature X-ray diffraction (XRD), scanning electron microscope (SEM) and variable temperature Raman spectra. The compound exhibits NTE properties in the orderly O′ phase crystal structure. When the temperature is from 293 to 759 K, the ceramic NdMnO₃ shows negative thermal expansion of −4.7×10⁻⁶/K. As temperature increases, the ceramic NdMnO₃ presents NTE property range from 759 to 1 007 K. The average linear expansion coefficient is −18.88×10⁻⁶/K. The physical mechanism of NTE is discussed and clarified through experiments.