Synthesis and characterization of the solid solution, Ca2-xMnxP2O7, 0<=X<=2 crystal structure of CaMnP2O7

The phases of the Ca2-x MnxP2O7, 0 less than or equal to x less than or equal to 2, system have been synthesized at 900 degrees C in the form of powder and analyzed by X-ray diffraction. The form, beta-Ca2P2O7, is stabilized in the domain, 0 less than or equal to x less than or equal to 0.275. A continuous solid solution has been identified for 0.65 less than or equal to x less than or equal to 1.05. The phases of composition, x greater than or equal to 1.80 are isotypical with Mn2P2O7. A single crystal X-ray diffraction study of material with x=1, of the domain, 0.65 less than or equal to x less than or equal to 1.05, shows it to be isotypical with Cd2P2O7: triclinic unit cell, P1 bar, a=6.562(3), b=6.604(3), c=6.610(3)Angstrom, alpha= 65.90(3), beta=83.49(4), gamma= 87.29(4)degrees, V=259.8(2)Angstrom(3), Z = 2, R=5.74/Rw=6.78% for 712 observed reflections (F>9.0 sigma(F)). The structure is formed of alternating layers of P2O7 and Mn2O10 groups, creating cavities in which the Ca2+ cations are found. These ions display seven-fold coordination with average Ca-O distance equal to 2.465(5)Angstrom. Mn2+ ions are found with octahedral coordination; average Mn-O distance, 2.235(5)Angstrom. P2O7 groups exist in eclipsed conformation.