New class of high-entropy pseudobrookite titanate with excellent thermal stability, low thermal expansion coefficient, and low thermal conductivity
Jinyu Wu, Xiaohui Ma, Xiaoxia Hu, Liwen Yan, Feng Hou, Jiachen Liu, Anran Guo
Abstract
Abstract As a type of titanate, the pseudobrookite (MTi 2 O 5 /M 2 TiO 5 ) exhibits a low thermal expansion coefficient and thermal conductivity, as well as excellent dielectric and solar spectrum absorption properties. However, the pseudobrookite is unstable and prone to decomposing below 1200 °C, which limits the practical application of the pseudobrookite. In this paper, the high-entropy pseudobrookite ceramic is synthesized for the first time. The pure high-entropy (Mg,Co,Ni,Zn)Ti 2 O 5 with the pseudobrookite structure and the biphasic high-entropy ceramic composed of the high-entropy pseudobrookite (Cr,Mn,Fe,Al,Ga) 2 TiO 5 and the high-entropy spinel (Cr,Mn,Fe,Al,Ga,Ti) 3 O 4 are successfully prepared by the in-situ solid-phase reaction method. The comparison between the theoretical crystal structure of the pseudobrookite and the aberration-corrected scanning transmission electron microscopy (AC-STEM) images of high-entropy (Mg,Co,Ni,Zn)Ti 2 O 5 shows that the metal ions (M and Ti ions) are disorderly distributed at the A site and the B site in high-entropy (Mg,Co,Ni,Zn)Ti 2 O 5 , leading to an unprecedentedly high configurational entropy of high-entropy (Mg,Co,Ni,Zn)Ti 2 O 5 . The bulk high-entropy (Mg,Co,Ni,Zn)Ti 2 O 5 ceramics exhibit a low thermal expansion coefficient of 6.35×10 −6 K −1 in the temperature range of 25–1400 °C and thermal conductivity of 1.840 W·m −1 ·K −1 at room temperature, as well as the excellent thermal stability at 200, 600, and 1400 °C. Owing to these outstanding properties, high-entropy (Mg,Co,Ni,Zn)Ti 2 O 5 is expected to be the promising candidate for high-temperature thermal insulation. This work has further extended the family of different crystal structures of high-entropy ceramics reported to date.