Investigation of the Vanadyl Bond Ordering and Analysis of the Spin Exchange Interactions in Pb₂V₃O₉ and Pb₂As₂VO₉

Abstract

The structures of Pb 2 V 3 O 9 and Pb 2 As 2 VO 9 were determined by X-ray diffraction to settle the issue concerning whether the arrangement of the V 4+ dO vanadyl bonds is ordered or disordered. The new crystal structure of Pb 2 V 3 O 9 refined by using a twinned crystal differs from the previous structure, determined from a combined use of powder X-ray and neutron diffraction data, and suggests an ordered Ferro arrangement of the V 4+ dO vanadyl bonds as does the Antiferro crystal structure of the new Pb 2 As 2 VO 9 . In Pb 2 V 3 O 9 , a triclinic f monoclinic transition is observed at 400°C, and the corresponding high temperature form was structurally characterized. The spin exchange interactions of Pb 2 V 3 O 9 and Pb 2 As 2 VO 9 were evaluated by performing qualitative spin dimer analysis based on tight binding calculations, and those of Pb 2 V 3 O 9 were also examined by quantitative mapping analysis based on density functional theory calculations. To a first approximation, the spin-lattice of Pb 2 V 3 O 9 is described by an alternating antiferromagnetic chain model, which is made up of the super-superexchange interactions mediated by VO 4 tetrahedra between adjacent chains of corner-sharing V 4+ O 6 octahedra. The magnetic property of Pb 2 As 2 VO 9 is predicted to be paramagnetic, in agreement with experiment.

Floating zone crystal growth and structural distortion of Pb2V3O9

“…As-grown samples were cleaved to appropriate size in paratone-N oil and mounted in a cryo-loop for data collection at 180 K. Larger crystals were evaluated and oriented using a custom 4-circle diffractometer with CuKa radiation. Refinement of the crystallographic data yielded results in agreement with previous reports [5]. However, inconsistencies in Table 3 and the supplemental data of this reference were noted, the supplemental data being correct.…”

“…2. The natural twinning of the crystals, described in detail by Mentre et al [5], limits single-crystal size to that shown in Fig. 2(a).…”

“…Differential scanning calorimetry (DSC) measurements were performed under flowing argon gas to obtain a more accurate value for the temperature corresponding to the monoclinic to triclinic structural phase transition previously reported [5]. Upon cooling, an exothermic peak with an enthalpy of À43(5) J/mol K is observed in the DSC signal at 759(1) K, see Fig.…”

“…5. Calorimetry allows for a more precise determination of the transition temperature than X-ray diffraction, where the transition temperature was ambiguous within a 100 K window [5].…”

Topology and symmetry analysis of the Sr2VO(VO4)2 family exhibiting magnetic properties and prediction of structures with different orderings of vanadyl bonds

“…After the structural modifications in the Srvanadyl-vanadate family were derived, the data on the preparation and studies of the Pb 2 V 3 O 9 and Pb 2 As 2 VO 9 structural modifications of an analogous lead family [6] were known for us. With consideration for an alter native choice of axes in the diffraction experiment in [6], the structure of Pb 2 As 2 VO 9 corresponds to the derived structure with space group Р2 1 /c.…”