CaO is doped at La site in LaGaO3 using solid state reaction method. During powder XRD analysis, the undoped sample (LaGaO3) was matched with ICDD card 01-089-7833 and it consist of sharp peaks for (200) and (020) peaks lying on the either side of highest intensity peak of (112). But with Ca doping, the peaks corresponding to (200) and (020) superimposed with (112) peak and intensity of doped samples also decreased.
I guess your un-doped LaGaO3 sample is well crystallized whereas the Ca-doped sample is not well crystallized. If you have only broad scattering with some humps then that is close to amorphous or with very small crystallites (nano-crystalline). You should be able to improve the samples by annealing.
What is the fraction of Ca doped with the LaGaO3.
Did you check the phase diagram?
probably some other phase formation takes place. It may also possible for more number of species form complex crystal structure, which make the system in the amorphous phase.
@Mahanty
The doping level of Ca is 5mol% in La1-xCaxGaO3.
Thanks you all.
I think in another way. Actually, in perovskite structure, all the oxygen lies at the face center positions forming GaO6 octahedra. So, with Ca doping, oxygen vacancy formation may take place, which may distort GaO6 octahedra. Also, (200) and (020) planes contain the octahedral oxygen. So, with Ca-doping, the reflection due to these planes is scattered and i get broad hump rather than peak. Also, the other planes in doped sample have sharp peaks with decrease in overall peak intensity. But, i do not have the literature support to make this claim. Please advise.
I think you have a general misunderstanding in the effect of distorted coordination polyhedra. It doesn't matter how much they are distorted from any ideal shape as long as they have all the same distortion, i.e. they have a well-developed translation symmetry. Then you will get also very sharp reflections. You can simulate this simply by changing the lattice parameters, e.g. simply the angles alpha, beta and gamma. Keep the relative positions of all atoms within the unit cell and you will observe that the structure changes, the peak positions will also change but not the sharpness and only slightly the reflex intensities as function of the Bragg angle (LPG correction). Since you don't change the atomic positions the structure factor will not change at all.
Difftraction has nothing to do with reflection in the sense of planar or less planar atomic planes. Crystal lattices are build up by lattice points which are usually mathematic abstractions of many atomes (cf. polymeres or proteines).
You will only observe reflex broadening if your mathematic lattice is distorted, e.g. as assumed by Tapan or Volker which assume lattice defects. Typical examples are topostractic effects in layered structures where at the same Bragg angle very sharp but also very broadened peaks may appear. I would expect that your Ca occupies preferred positions and causes for certain planes a partial desctruction of your translation symmetry. This will effect all reflections in a different manner.
Dear Dr Nolze
Thanks for the advice. Please refer me some papers so as to get better understanding.
simply "google" the term: anisotropic peak broadening. There appear numerous papers describing the effect and proposeing models to consider it during full-pattern/Rietveld refinement.
intensity change means adsorption on surface while change in theta indicate inter-layer change. intensity change also affected by concentration of dope material.
sheet 2 indicates change in intensity of some peak after bentonite clay treated with NaCl
@ A. Desai: There are many factors which affects the intensity of an interference (commonly but unfortunately described as reflection although there is no reflection at all :-) ). You can find all the factors described in detail in any book about diffraction.
Moreover, you shouldn't define terms like inter-layer. I guess you are talking about interplanar distance which is related to lattice points, i.e. a mathematical construction of a commonly 3-dimensional, periodical arrangement of the same motif (represented by a lattice point). Layers are usually used to describe layers of atoms, i.e. real-existing physical objects.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Material Characterization