HARDNESS AND FRACTURE TOUGHNESS OF CALCIUM-DOPED MEDIUM- ENTROPY PEROVSKITE OXIDES

Author

Arjit Mani Dhakal, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2025

Degree Name

Master of Science

Department

Mechanical Engineering

First Advisor

Swift, Geoffrey

Abstract

Advanced ceramic materials exhibit superior mechanical properties for a range of technological applications. However, the mechanical properties, particularly hardness and fracture toughness, of perovskite materials, which are crucial for various applications, remain largely unexplored. In this research, the macro-indentation Vickers hardness testing of a series of calcium- doped medium-entropy perovskite oxides (ABO3) with lanthanum as A site cation and iron, chromium, nickel, and cobalt as four different B site cations in various combinations, is carried out. Through macro-indentation with a load of 49 N and a dwell time of 10 sec, the hardness of sixteen medium entropy perovskite oxide (MEPO) samples with calcium doping ranging from 0-30 mol%, was evaluated. The fracture toughness was calculated by analyzing the crack length emanating from Vickers indentations using optical microscope. The mechanical properties varied significantly as per the transition metal combinations and calcium doping levels. Amongst the four MEPO systems, System 1 (Cr-Fe-Ni) exhibited the highest hardness of 9.66 GPa at 10 mol% Ca doping and the peak fracture toughness of 2.51 MPa·m¹/² at 20 mol% Ca doping. In contrast, System 4 (Fe-Ni-Co) revealed the lowest hardness of 6.10 GPa for the undoped sample and the lowest fracture toughness of 1.81 MPa·m¹/² for 20 mol% Ca doping. Several factors like densification, grain size change, oxygen vacancy concentration, and secondary phase formation led to variation in the mechanical properties among the systems. The Cr-containing perovskite systems generally outperformed others, highlighting its importance in applications requiring mechanical robustness and integrity.