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Piezoceramics enable interconversion between mechanical and electrical energies. They have found a plethora of applications in the automobile industry, medical diagnostics, and microelectronics, with PZT (Pb(Zr, Ti)O3) ceramics dominating the market. However, increasing environmental concern associated with the Pb involved has triggered extensive studies on lead-free alternatives, such as NBT-BT-KNN ((Na1/2Bi1/2)TiO3-BaTiO3-(K1/2Na1/2)NbO3) ceramics. One intriguing fact is that NBT-BT-KNN ceramics may generate giant strains through field-induced structural transitions from a "relaxor" state to a ferroelectric phase. However, fatigue inevitably occurs in piezoceramics from long-term functioning, exhibiting deteriorated ferroelectric properties or even critical breakdown under high voltage. Unlike ferroelectrics, the distinct structural transitions these relaxors undergo as a consequence of field or temperature changes, which are crucial fatigue influencing factors, complicate and inevitably impact fatigue behaviour in this class of ceramics. To date, there is a lack of knowledge of the fatigue mechanisms in these relaxors.In this thesis, phase transitions of the NBT-BT-KNN system are explored through the construction of electric field-temperature phase diagrams for three model compositions. The canonical relaxor compositions underwent ferroelectric phase evolutions influenced by both temperature and field, while the noncanonical relaxor showed spontaneous relaxor-ferroelectric crossover without an electric field. Based on this structural information, electrical fatigue behaviour was investigated by varying field amplitude, temperature, the polarity of fatigue waveform, and level of point defects for a thorough understanding of fatigue. The results underpinned the roles of reversible and irreversible fatigue which dominated at different fatigue stages. Furthermore, by employing chemical characterisation, the existence of a surface layer and its behaviour in fatigue wa

Clinically, decreased bone content surrounding implants, renewed pain and implant loosening lead to revision surgeries following fracture fixation and joint replacement. A key reason for this phenomenon is stress shielding by Wolff’s law where the high stiffness of the implant materials used results in under loading and resorption of the surrounding bone. What remains to be understood however is how implants of increased stiffness affect bone structure, mechanical properties and biology. To study these effects, an in vitro proof of concept was first conducted in which bone loads and three point bending stiffnesses were shown to increase with increased implant stiffness. Subsequently, 1.1 mm implants with roughened ends were made from nitinol, titanium and stainless steel Kirschner wires. Finally, an in vivo study was conducted on rats in which femora were either left intact, operated on or operated on with a nitinol, titanium or stainless steel wire inserted to evaluate the interrelated effects of bone remodelling.It was discovered that both surgery and implantation negatively affect bone length and isthmus with surgical trauma, implant composition and implant stiffness identified as key factors associated with altered growth plate activity as well as bone remodelling towards and into the intramedullary canal. Similarly, decreased trabecular bone presence and structure were noted however natural aging, surgical trauma and implant material properties all impacted the degree of change to trabecular architecture. Cortical bone structure was also affected with enhanced regions of empty osteocytes and increased periosteal bone deposition dependent upon surgery and implant properties although natural increases in porosity were also observed. Nanoindentation results further indicated the mechanical loads placed on the bone after surgery resulted in changes in bone stiffness at a localised, region based level with respect to time. This was true even for non-implanted contra