ESR Study of the Crystallographic Phases in Zn2P2O7:Mn and Zn2P2O7:Cu

The ESR spectra of Mn++ and Cu++ in Zn2P2O7 have been studied between room temperature and 200°C. A first-order phase transition is found at 132°C and a transition of higher thermodynamic order occurs near 155°C. The space group of Zn2P2O7 above 155°C is determined to be C-2/m, whereas between 132° and 155°C it is C-m. The value of | D | in the spin Hamiltonian for Mn++ ranges from 612 to 1319 G with nearly isotropic g values. The g values for Cu++ indicate an anisotropic environment with nearly axial symmetry about the z axis. The spectral lines of Zn2P2O7:Mn++ are broadened near the upper transition with the broadness dependent upon the particular electronic transition involved. This phenomenon is discussed in terms of possible mechanisms for the upper phase transition.