I have stabilized tetragonal phase of solid electrolyte at room temperature and this phase is fully ordered at RT. But it is found to be disordered tetragonal beyond ~450 deg. C. this order- disorder transition can be seen in variable temperature neutron diffraction patterns not in XRD.
X-ray and neutron diffraction are complimentary probes and should be used judiciously. One must know the basic principles of these two techniques. The main characteristic of X-ray diffraction is that since X-rays are scattered from electrons, the scattering power (form factor) is proportional to the number of electrons in the atom, it increases linearly as a function of Z, the atomic number. The neutrons are scattered from the nuclei of the atoms and their scattering power is not a smooth function of Z, there are many sudden variations specially for different isotopes of the same atoms. If you have H atoms in presence of heavy atoms like rare earth or actinides then the scattering from the H atoms is completely masked by the huge scattering from the heavy atoms in case of X-ray scattering whereas for neutron diffraction this is not so. Again scattering power of H and deuterium is not only different in magnitude but also different is sign. So if you have H atoms in your structure that participate in the order-disorder transition then you will see the transition much better in neutron diffraction. This is also so for O atoms. Also order-disorder transition is associated with dynamics and this can be much better studied by inelastic neutron scattering because the energy of thermal neutrons is of the same order of magnitude of the atomic dynamics. But again you should not underestimate the power of X-ray diffraction technique. Historically much of the physics of order-disorder transition has been successfully studied by X-ray diffraction in favorable cases.
By the way how do you know the phase transition in your sample is order-disorder type and not displacive type. It is not easy to distinguish these two types of phase transition.
The question is missing the essential information of the chemical composition of the compounds under study. This might be the fault of ResearchGate, though, which often changes the text of the question without giving you any warning.
In any case, based on your featured publications we are in the field of Co-Ni double substituted bismuth vanadates. In particular for this pair of elements,Co-Ni, the difference in scattering length is humongous for neutrons, while being nil for x-rays.
Niayazi talks about tetragonal phase of solid electrolyte. Has that anything to do with Co-Ni double substituted bismuth vanadates?
Niyazi talks about tetragonal phase of solid electrolyte. Has that anything to do with Co-Ni double substituted bismuth vanadates or whatsoever?
The order- disorder transition of stabilized tetragonal phase in BiMeVOx solid electrolytes have been proven by using DSC and AC impedance spectroscopy. In BiCeVOx and BiHfVOx system I noticed in variable temperature XRD analyses some evidences for the existence of this type of transitions, e.g., the disappearance of some XRD peak satellites during the refinement of XRD patterns in addition to a remarkable change of some superlattice peaks in the XRD pattern collected at temperature near to the onset temperature of this transition as estimated form DSC and Arrhenius plots of conductivity. In contrast, XRD analysis showed no evidence neither for Co-Ni nor for Cu-Mg double substituted system. It is well- known that such order- disorder transition in this family of oxides is associated with a subtle change in oxygen sublattice positions with increasing temperature. Is this attributed to the ionic radii of Me dopant or to the the double substitution? Can this point be revealed using neutron diffraction analysis?
Daniel has already pointed out that in Co-Ni system neutron can be very useful because their neutron scattering lengths are very much different. The coherent neutron scattering lengths of Co and Ni are 2.49x10^-13 and 10.3x10^-13 cm, so difference in scattering length is quite large. So if you have some reflection (in ordered phase) whose structure factor is expressed as the difference in their scattering lengths then you will observe superlattice peaks in neutron diffraction whereas in X-ray diffraction their intensities would be vanishingly small. For Cu-Mg system however you may observe such reflections X-ray diffraction because the number of electrons are quite different for Cu and Mg. You should also see such reflections in neutron diffraction as well. In any case it would be useful to study this phase transition by neutron diffraction. Also you will get much better information about the O positions from neutron diffraction.
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