Silver-gadolinium polytetraphosphate AgGd(PO3)4 synthesis, structural study, IR spectroscopy and conductivity investigation

Crystals of a new silver-gadolinium, AgGd(PO3)4, have been synthesized for the first time by a flux method. The structure [monoclinic, P21/n, a = 7.2378(2) Å, b = 13.0913(5) Å, c = 9.8136(4) Å, β = 90.494(1)°, V = 929.83(6) Å3 and Z = 4] was solved by a three-dimensional Patterson function and refined to R1 = 0.0399 (wR2=0.0885)(wR2=0.0885) on the basis of 3270 unique observed reflexions using 164 parameters. AgGd(PO3)4 is isostructural to NaLa(PO3)4, AgLa(PO3)4 and AgNd(PO3)4. The structure is based upon long chain polyphosphate running along the shortest unit-cell direction and made up of PO4 tetrahedra (with a period of four tetrahedra) sharing two corners, linked to the polyhedra of gadolinium and silver by common oxygen atoms to the chains. This type of organisation gives rise to a three-dimensional framework. Gadolinium atoms have an eight-fold coordination while silver atoms have approximately six oxygen neighbours. Infrared spectrum of AgGd(PO3)4 at room temperature, investigated in the frequency range 400–1500 cm−1, confirms the atomic arrangement within the structure. The electrical conductivity of AgGd(PO3)4 has been measured on pellets of the polycrystalline powder and evaluated as a function of temperature. The conductivity of this phase was quite low and the values of 4.01 × 10−7 and 1.10 × 10−6 Ω−1 cm−1 were obtained at 803 and 873 K, respectively.