Anomalous thermal expansion properties in perovskite Sm0.85Zn0.15MnO3
Abstract The multiple sintering compounds of perovskite Sm0.85Zn0.15MnO3, which are denoted as S1, S2, S3, S4, and S5, have been synthesized by a solid-state method. The analysis of their crystal structure and microstructure were conducted by X-ray diffractometer and scanning electron microscopy, respectively. The average particle size and porosity were counted by microscopic image analysis. The thermal-expansion behavior of the compounds was studied by a dilatometer and high-temperature XRD. Experimental results indicated that the once sintering sample (S1) of Sm0.85Zn0.15MnO3 possesses the negative thermal expansion (NTE) properties with a coefficient of thermal expansion of −8.40 × 10−6 K−1 in the range of 519–1023 K. By contrast, the thermal expansion behavior for the multiple sintering samples (S2–S5) is not same as that of S1. The porosity of the samples dramatically affects their thermal expansion behavior. The samples S1 and S2 exhibit the NTE characteristics as their porosity was larger than 9.5%, but the samples S3, S4, and S5 exhibit positive thermal expansion characteristics, as their porosity is less than 9.5%. In addition, anisotropy of thermal expansion plays a crucial role in the NTE mechanism. The mechanism underlying the NTE of Sm0.85Zn0.15MnO3 (S1) involves the coupling effect of the high porosity and the microstructural NTE effect caused by crystal grains with anisotropic thermal expansion and intercrystalline pores.