Synthesis, crystal structure, and magnetic investigations of FePb 1−xBa xP 2O 7 (0≤x

Abstract

The new solid solution Fe(Pb 1−xBa x)P 2O 7 has been synthesized by solid reactions. In the whole experimental range (0≤x<1 ; T=850 °C), this solid solution is isotypic to the pure phase FePbP 2O 7 and closely related to αCa 2P 2O 7. The structures of FePbP 2O 7 ( x=0) and FePb 0.2Ba 0.8P 2O 7 ( x=0.8) have been determined from a single crystal and refined to R=0.041 and R=0.034, respectively. FePbP 2O 7 and FePb 0.2Ba 0.8P 2O 7 crystallize in the monoclinic space group P2 1/n, with a=5.3800(11) Å, b=8.3100(17) Å, c=12.800(3) Å, β=91.00(3)° and a=5.5333(2) Å, b=8.4196(3) Å, c=12.8238(2) Å and β=91.16(2)°, respectively. The most salient feature of the FePbP 2O 7 structure is the presence of an isolated 4+1 square pyramidal site occupied by Fe 2+. The connections between FeO 5 units and P 2O 7 diphosphate groups define tunnels along [100] where Pb 2+ cations are located and give rise to a three-dimensional framework. The cationic distribution (Pb 2+, Ba 2+) has been determined for the isostructral compounds Fe(Pb 1−xBa x)P 2O 7 (0≤x<1). FePbP 2O 7 is antiferromagnetic : T N=10 K; this is consistent with the fact that the magnetic interactions arise only from the Fe–O–P–O–Fe superexchange mechanism.