I am doing research on co-doping in scandia stabilized zirconia. A decrease in lattice parameter is observed after pressureless sintering at 1600 degC compared to that of powder.
After spark plasma sintering at 1250degC, the lattice parameter is observed to be lesser than that of pressureless sintering.
What might be the reason for this?
the system is YbScSZ (mol% of Yb
i think it can be due to recrystallization reaction (annihilation of line defects)
Dear Isha, ''Zirconium dioxide is one of the most studied ceramic materials. ZrO2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal ( 1170C2370C) at higher temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces large stresses, and these stresses cause ZrO2 to crack upon cooling from high temperatures. When the zirconia is blended with some other oxides, the tetragonal and/or cubic phases are stabilized. Effective dopants include magnesium oxide (MgO), yttrium oxide (Y2O3, yttria), calcium oxide (CaO), and cerium(III) oxide (Ce2O3).''
That means stabilized Zirconia has much smaller lattice parameters, and therefore their spectral lines ships towards the higher angles according to:
Del d /d = - Cotan (Theta) Del Theta.
The shift increases with theta values that is the clear indication of the increase is due to the lattice parameters.
Dear Isha,
You did not mention your compostions, which matters.
Before considering special effects on the lattice parameters, examine available phase diagrams of ZrO2 and your codopants.
Are you in a single phase region for both temperatures 1250 and 1600°C or
the material at 1250°C contains other modifications? The sintering temperature 1250°C can be rather low for uniform distribution of dopants.
I have found a paper that describes an opposite effect of increasing lattice parameter of the cubic phase in a 10 mol % Sc2O3 – 1 mol %CeO2 – ZrO2 Ceramics with increasing sintering temperature (see a link).
http://research.cecs.ucf.edu/chea/pdf/14.pdf
I agree with Mark,
what's your system?
you can check in the phase diagram where is your point.
It is clear that the SPS-process, which is usually shorter in time, does not allow to reach the equilibrium in your system, i.e. accomplish the solid state dissolution process there completely.
(CaO-Fe2O3) volume of unit cell increases with increasing sintering temperature, this is also proof with JCPF card. BUT reason behind this i am not able to explain. kindly help me . Dr. Mark is giving a link but it is not opening.
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