In principle, yes, you keep your sample a constant temperature and you quote the lattice parameter value at that temperature.
In practice, it depends. How many significant figures will you have in your lattice parameter? That will depend on how good your angle calibration is and how precise your peak angle values are. How much variation in temperature are you considering. If your temperature will vary by plus or minus a degree C, that will alter your lattice parameter by about 10 - 30 parts per million, typically for many materials. So if you are wanting 4 sig figs in your LC, then a few degrees won't matter. If you want 6 sig figs (and yes, many common lab instruments - nothing fancy - can provide this), then you should control the temperature to 0.1 deg.
Dear BB
Yes, it is important to maintain a certain temperature when calculating the lattice constant from XRD. This is because the lattice constant is a measure of the distance between atoms in a crystal lattice, and temperature can affect this distance. As temperature increases, the lattice constant will increase, and as the temperature decreases, the lattice constant will decrease. Therefore, it is important to maintain a consistent temperature when measuring the lattice constant in order to ensure accurate results.
Hi B.Bhaskaran,
I fully Concur with R. Sagayaraj ,added to this following data helps you to better understand this:
A Ni3Al-based alloy Cold rolled samples were isothermally annealed for 1 h at 700, 800, 900,1000 and 1100 deg C and Crystal sizes(lattice parameter: a) are determined
700 C :- 63.29nm
800 C :-103.09nm
900 C :- 135.13nm
1000 C :- 188.67nm
1100 C :- 204.06nm
From the above you can clearly see that lattice constant is temperature dependent and therefore it is essential to carryout XRD experiment at constant temperature to obtain consistent lattice constant values.
Reasoning Analogy: Coefficient of Thermal expansion(alpha : on macroscopic scale)and lattice constant( a : on crystal structure scale) are temperature dependent,increases with increase in temperature and vice versa.
[also Diffusion is temperature dependent and varies as per Arrhenius equation]
the following reference might help you to fully grasp and appreciate understanding of XRD study.
thanks & regards
g.sudhakar
phd(materials engineering)
hcu.
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