I collected a diffraction pattern by XRD powder system from a new EBPVD YSZ TBC surface. I thought to obtained a tetragonal zirconia pattern with an preferred orientation caused by the deposition method but I thought that the peaks position are the same.
Instead in my XRD pattern I have only few tetragonal peaks with a completely different height respect of the reference pattern; other peaks, present in reference pattern and in APS TBC are completely absent. I have also some little peaks that are absent in t-zirconia reference pattern and in APS TBC.
have someone information about EBPVD TBC XRD pattern and the evolution of crystallographic phases? are different from APS system?
which kind of reference pattern can I use to index the EBPVD TBC pattern?
Thanks for your help!
From what I see, I believe your diffractogram is compatible with an extremely strong preferential orientation, with the (110) planes of the tetragonal phase parallel to the surface (they correspond to the (100) planes of the parent cubic phase). This could explain why you have only the 2 big peaks: they correspond to the (110) and (220) planes, the small shoulders on their respective left beeing (002) and (004).
The other peaks are absent because the whole material is oriented the same way. This is almost like a single crystal, but with possible rotations around the c-axis (perpendicular to the surface) that can not be detected by XRD.
As for the very small peaks, I'm not sure. You may want to check if the small one around 32° is not a Kbeta residue (the (110) planes diffracting with the CuKbeta radiation), but I have no idea for the one around 66°.
Hope that helps...
PS: of course, this is valid if you used Cu Kalpha radiation!
Hello,
I'm not very familiar with EBPVD, but I see only few explanations for your problems:
1- you may see the substrate through the TBC (possible if the coating is thinner than ~5µm)
2- because of high temperatures, you may have high residual stresses after the process, and form a "more exotic" phase of zirconia, one of those who appear at high pressure (orthorombic). Residual stresses may also cause a shift of the peaks positions, even if the phase remains tetragonal.
3- if you have a preferential ortientation, that may explain also why the heights of the tetragonal peaks are very different from the reference peaks.
Good luck!
Could you post an image of the diffractogram? It is hard to speculate how big are the differences. All modifications - except of the monoclinic - are quite similar and hard to seperate froom each other. Thanks!
I attach here the overlapping of EBPVD and APS XRD patten and I indicated on the image the tetragonal peaks (on the basis of reference pattern for YSZ with 8% of Y2O3). I have seen the different height for the peaks at 35 and 75° causing from preferetial orientation but other tetragonal peaks are absent. Moreover I have also other peaks that I don't know where coming from.
From what I see, I believe your diffractogram is compatible with an extremely strong preferential orientation, with the (110) planes of the tetragonal phase parallel to the surface (they correspond to the (100) planes of the parent cubic phase). This could explain why you have only the 2 big peaks: they correspond to the (110) and (220) planes, the small shoulders on their respective left beeing (002) and (004).
The other peaks are absent because the whole material is oriented the same way. This is almost like a single crystal, but with possible rotations around the c-axis (perpendicular to the surface) that can not be detected by XRD.
As for the very small peaks, I'm not sure. You may want to check if the small one around 32° is not a Kbeta residue (the (110) planes diffracting with the CuKbeta radiation), but I have no idea for the one around 66°.
Hope that helps...
PS: of course, this is valid if you used Cu Kalpha radiation!
Hi, for the peaks that you don't know where they come from, you may also pay attention to the influence of substrate (or bond coat between the substrate and the top YSZ coat) on the XRD pattern of the TBC produced by EB-PVD. What is the material of substrate and bond coat? Nickel based superalloys? How about the thinkness? The TBCs produced by EB-PVD are generally not very thick, so the XRD pattern sometimes contain information from substrate or metallic bond coat. You may check this.
Good luck!
Laurant, you are right. The big peaks are K alpha peaks and the tiny peaks (31 and 66 degrees) are K beta. There is only one aspect where I do not agree. If you see 002 and 004 as well it cannot be a single crystal. So we see either an epitaxial layer or a strong {110}- fibre texture.
Epitaxial growth: Since the misfit between {110} and {001} is very small we have two orientations which grow simultanuously. However, since the 00l should have the half intensity because of its multiplicity (see the "ideal" diffractogram behind) it seems that the majority of crystals ar grown with the {110} surface. Only a small amount is grown parallel to {001}.
The fibre texture is also an option which cannot be automatically excluded. But it is possible to test this. Either you are doing a scan which is slightly asymmetric, i.e. tilt your sample (by a small wedge), or switch off the theta movement of the sample. If it is a single crystal you get no or only a much smaller intensity for 110 and 002. If it is a fibre texture you could use a theta (or sometimes this axis is also called omega) which is in reflection for one of the other peaks (in case you can use fixed theta). Then you only need to scan the angle area for the respective reflection.
One question: What is your substrate? The orientated growth shouldn't work if your substrate is not single-crystalline.
Still another question: Do you have any idea about the intensity edge near 34 degrees? It looks like that the entire small angle area below 34 degrees has a smaller intensity,
I believe that this intensity edgeat ~34° is due to a Nickel filter (that should remove most of the Kbeta radiation): I think the edge on the diffractogram corresponds to the Ni absorption edge: I'm not completely sure about it, but I believe that between the high peak at 35-36° and this edge at 34° part of the background is in fact due to the diffraction of the "brehmstrallung" (the white part of the emission spectum of the Xray tube) by the (110) planes. Below 34° (or the corresponding wavelength diffracted by the (110) planes) the Ni filter absorbs also this "white" diffracted intensity..
You can see the same edge at ~72°, and this corresponds to the same phenomenon but for the intensity diffracted by the (220) planes.
So in both locations we can distinguish the same sequence: with growing diffraction angl, very small Kbeta peak, absorption edge of the Ni filter, large Kalpha peak.
These artifacts would not be seen with a real monochromator that disperses wavelength instead of absorbing them...
Good point! And you don't see it in the other diffractogramm because of the very strong reflection of the 110 ?
BTW: There exists no (220) plane. It is the second order reflection of the (110) plane called 220. Lattice planes have go through lattice points but there are no lattice points.
That's right. On the other diffractogram, you see (or guess) an adge at around 26-27°, corresponding to the (101) peak.
And you're right, there is no physical (220) plane. Let's say it's a convenient description of the second order "reflection" of the (110) plane. Even if some people say that a family of reticular planes have to contain all lattice points, but some planes in the family may not contain lattice points... From my point of view this is a philosophical question that I prefer not to get in too deeply!
Some information about my analysis: I used Cu Ka radiation and I have the Ni filter. the thickness of my TBC coating is about 200micron, so I don't expect contribution by substrate (NiCoCrAlY coating). I check the Kbeta contribution of the peaks at 35 and 75° and you are agree: the little peaks at 31 and 66° are the Kbeta of (110) and (220). Thanks a lot at all for your help!
About the evolution of EBPVD, do you expect the same behaviour of APS (with cubic and monoclinic transformation)?
Sorry, I know a little bit of zirconia and X Ray Diffraction, but nothing at all on EBPVD and APS...
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