Simultaneous two energies anomalous scattering for the study of the dynamics of structural transformation

In this work the wiggler of VEPP-3 is used for the generation of two beams of synchrotron radiation. After the focusing monochromator, both beams have an energy near the Ni K-edge; they differ by 20 eV. At the sample position the two beams are separated by 2.3 mm. The simultaneous registration of two X-ray diffraction patterns at different energies was made by two position sensitive detectors OD-2. A comparison of the two diffraction patterns, registered at different energies, clearly shows the anomalous scattering effect for the test sample NiO. This method was used for the investigation of the behavior of the Ni atom during the solid state chemical reaction NiO + MoO3 → NiMoO4 at T = 600–800°C. This method gives an anomalous scattering signal when the Ni atoms appear in the molybdenum oxide phase. The kinetics of formation of β-NiMoO4 was obtained. At different temperatures the Ni atoms occupied different positions in the β-NiMoO4 structure, at 650°C they were at the sites of the crystal lattice, at 690°C they were in the interstitial positions.