I have a Heusler Alloy thin film sample which consists of cubic and tetragonal phases at room temp. Now doing the measurement at low temperatures the XRD peaks due to the cubic phase remain at the same position but the tetragonal peak shifted towards lower angle in a systematic way. But there is no change in the shape and amplitude of the tetragonal peaks. what is the reason behind this?
Post your XRD data and the instrumentation used.
Dear Ravi Sir,
I also observed similar things. The XRD peak in my sample shifts to higher 2theta on increasing the annealing temperature.
Film thickness-40 nm
Si and MgO substrate
Single crystalline
Second thing I observed is it shows huge change in the intensities of substrate peak on changing annealing temperature.
How about this explanation?
The substrate has larger thermal expansion rate than the film. When it’s cooled down, the film is compressed in the plane direction, consequently the film expand in the perpendicular direction (XRD measuring direction) due to the Poisson ratio. And the cubic and the tetragonal crystals have different thermal expansion rates.
I also experienced similar thing. Each peaks from a metal film sample showed slightly different lattice parameters. I guess it was due to mismatch of thermal expansion between the deposited film (Pd) and the substrate (SiO2) and anisotropy of thermal expansion in Pd crystal. Maybe, the thermal expansion rates are different in 100 direction and 111 direction.
Oooop! Not only different thermal expansion rates but different elastic properties (Young's modulus) is the explanation. For my expience case, not "anisotropy of thermal expansion" but "anisotropy of elasticity" is right one.
Sorry!
Dear Dr. Yoshiki Fukada,
I appreciate your answer. Can you please upload any article regarding the argument.
Please post your data Shalu!
The information you provided regarding your samples is critical to any conclusion regarding the correlation of Nano structure with XRD data. There is a very nebulous line between "highly oriented" poly crystalline materials and "highly miss-oriented monocrystalline" materials as far as the spatially blind conventional diffractograms are concerned. You'd need to view the 2D reciprocal space to perceive that. See example below for the NIST2000SRM.
Do post this as a new question on RG and then post a link here to make it easy to contribute. So that it may not be perceived as "raining on Nirmalendu's parade" :-)
https://www.researchgate.net/post/What_is_the_best_way_to_interpret_REAL_TIME_3D_X_Y_o-2TH_o_ph_ch_reciprocal_space_relative_intensity_data_from_HRXRD_rocking_curve_analyses
Dear Nirmalendu Patra
The shift of 2theta value to lower value and sometimes to higher value may be attributed to the change to the value of the stain, which can be defined in terms of the change into 2theta value from the original 2theta value of the cards dividing to the original 2theta value. So the strain may be negative or zero or positive. In your case I expect that a contraction occurs in the planes due to lower temperature and the strain becomes negative value. So, I advise you that you should calculate the strain.
Dear Nirmalendu Patra
Sorry for my rate respons. Though I did not mention about the penomenon, there is example data showing it.
https://www.researchgate.net/publication/312218112_sav_paper_reviced_submit
You can see each peaks from Pd slightly shift each other and there is a tendency that the peaks from 200, 400 and 311 appear at lower angle and the peaks from 111, 222 and 331 appear at higher angles.
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