Mechanical Behaviour and Fracture Mechanics of Praseodymium Modified Lead Titanate Ceramics Prepared by Solid-State Reaction Route

The praseodymium modified lead titanate ceramics with composition where = 0.04, 0.06, 0.08, and 0.10 prepared by solid-state reaction technique were subjected to indentation induced hardness testing method. The indentations were induced in the applied load ranging from 0.245？N to 4.90？N. The microhardness varies nonlinearly with load and was best explained by the concept of Newtonian resistance pressure as proposed by Hays and Kendall’s law. Crack propagation, fracture toughness ( ), brittleness index ( ), and yield strength ( ) were studied to understand the effect of Pr content on various mechanical parameters. The load independent values were found to increase with the increase in praseodymium content. 1. Introduction Ceramics are generally associated with distinctive problems, some uniquely beneficial and restrictive which determine the materials utilities, among these are hardness, brittleness, and fracture toughness. The measured hardness of a brittle material as determined by conventional tests (Vickers, Knoop, Rockwell, etc.) is a measure of materials resistance to deformation, densification, displacement and fracture. Conventional hardness measurements, which depend on size of an indentation resulting from an applied load, are load independent. This is especially noticeable at lower indentation loads where most measurements are made in order to avoid experimental problems associated with fracture. Local fracture around and under an indentation can affect the depth of penetration or size of the indentation and thus can be considered an intrinsic part of the indentation process. Fracture can also create practical difficulties in making hardness measurements because cracking at indentation corners or fragmentation can hamper hardness measurements. The degree of fracture at indentations in ceramics is load dependent. Low loads are associated with deformation while fracture is conspicuously more prominent at high loads. Microindentation technology has been used for the measurements of fracture toughness of ceramic materials by Evans and Charles [1]. Generally, the dielectric, piezoelectric, elastic, and mechanical behavior of ferroelectric ceramics depend in a complex way on microstructural parameters such as porosity, grain size, and grain boundary effects. The properties of ferroelectric ceramics are also very sensitive to temperature, to stress and strain, to frequency, and so forth. Lead titanate (PbTiO3) is well known as a perovskites type ferroelectric material with a high Curie point ( ) of 490°C. A phase transition from the paraelectric