<P> Single crystals of Zn2P207 containing 0.1% by weight of manganese impurity or 0.04% by weight of copper impurity were studied by means of electron spin resonance techniques from room temperature up to about 200°c. </p> <P> The existence of a phase transition at about 132°C in Zn2P2O7 was confirmed and a new phase, existing between 132°C and 155°C was found. The space group of the unit cell in this phase was deduced from the esr measurements. The spin Hamiltonian parameters were measured in the three phases and a discussion of their significance in terms of current theories of the zero field splitting of the ground state of S-state ionsis given. </p> / Thesis / Doctor of Philosophy (PhD)