The effect of ferroelastic domains and ultrahigh‐density dislocations on fracture toughness of high entropy niobates
Panpan Wang, Huangyue Cai, Muzhi Li, Lirong Luo, Xiaofeng Zhao
Abstract
Abstract This study investigates the fracture toughness and toughening mechanism of (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Y 0.2 )NbO 4 , a high entropy material characterized by a high thermal expansion coefficient and low thermal conductivity. Our finding demonstrates a noteworthy 50% increase in fracture toughness for (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Y 0.2 )NbO 4 (∼3.09 MPa m 0.5 ) compared to YNbO 4 (∼2.11 MPa m 0.5 ). The superior fracture toughness for (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Y 0.2 )NbO 4 can be attributed to the two key factors: relatively easy ferroelastic domain switching and the presence of ultrahigh‐density dislocations (∼7 × 10 8 mm −2 ). The enhanced ferroelastic toughening in (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Y 0.2 )NbO 4 is associated with its distinct characteristics, large atomic radius ( R A ), significant tetragonality ( c / a ratio), and low monoclinic β angle. These factors contribute to larger spontaneous strain, larger coercive strain, and lower transformation strain, respectively. These properties facilitate the formation and switching of the ferroelastic domains. In addition, the interactions between the large strain field surrounding the dislocations and the cracks facilitate crack deflection and bridging. The combined effect of ferroelastic toughening and ultrahigh‐density dislocations ultimately leads to the significant improvement in the fracture toughness of (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Y 0.2 )NbO 4 .