The fundamental properties of photorefractive crystals have been extensively investigated for nearly the past two decades. Two significant photorefractive crystals that have been the subject of investigation are bismuth silicon oxide (BSO) and barium titanate (BaTiO3). The aim of this thesis was to find ways to enhance the photorefractive properties of BSO and BaTiO3 to further research into production of a practical phase conjugate device with a high diffraction efficiency, fast response time, operation in the infra-red for laser diode compatibility, stable output and miniaturisation of crystal volume. A technique to enhance the diffraction efficiency of BSO by a factor x100 has been successfully demonstrated and waveguides have been successfully fabricated in BaTiO3 through H+ implantation. The losses of these waveguides have been minimized by implanting over a range of doses and measuring the observed losses. Both self pumped and mutually pumped phase conjugators have been successfully demonstrated in these BaTiO3 waveguides. However, the remaining concern is that BaTiO3 crystals in both bulk and waveguide geometries exhibit instabilities which are undesirable for stable phase conjugate output. Much speculation has been given to the nature of the instabilities, but it is shown for the first time, that under certain conditions the phase conjugate output makes a transition from stable to chaotic behaviour. Regions of stable operation have been identified.