X-ray Laue microdiffraction (µLaue) is a well-established technique to characterize microstructural and mechanical fields in polycrystalline specimens at the sub-micron scale with a strain resolution as high as 10^-4. Without any particular sample preparation, this non-destructive technique is suited for ceramics studies to obtain orientation and strain maps [1]. Complex Laue patterns from polycrystalline materials can be indexed rapidly thanks to the open source LaueNN software based on neural network recognition of Lauespot corresponding hkl Miller indices [2]. To complement standard Laue measurements, additional experimental Laue spot energy determination provides the local stress tensor [3] and depth resolution can also be reached for 3D mapping [4]. Moreover in situ or operando experiments can be carried out. We present here a new and unique µLaue setup located on CRG-IF BM32 synchtrotron beamline at ESRF [5] for in situ high temperature materials investigations as high as 1500 K integrating a modified QMAX furnace [6]. To ensure the structural parameters determination accuracy, we correct for any parallaxe issues on the scattering angles measurements due to the sample and furnace differential expansion during heating or cooling steps. We develop hence a methodology to calibrate the setup geometry using a reference single crystal whose lattice parameters variations with temperature are known, here a piece of sapphire [7]. Also, we report the experimental determination of the temperature at the closest to the specimen top surface [7] which is required for precise phase transition studies.
A first application to the in situ observation of high temperature phase transition in a bulk ceramic material made of plenty of nanosized pure zirconia crystals is presented [7]. A region originally containing a single cubic crystal at very high temperature, and composed 3 tetragonal or 24 monoclinic variants at high or room temperatures respectively, was selected by means of an optical microscope. Raster scans were performed at different temperature and paying particularly attention on recording sample map close to the temperature of monoclinic to tetragonal transition. Since Laue pattern is featured by crystallographic symmetries, a change of Laue spot shape is clearly visible: in low temperature monoclinic structure each Laue spot is crowded by multiple tiny or diffuse spots corresponding to the superimposition of numerous individual nanocrystals scattering signals, whereas for high temperature tetragonal one Laue spot is sharper in size. Average elastic lattice parameters can be determined from the Laue pattern analysis by assuming a single crystal model. Finer analysis are ongoing to extract broader insights on the distributions of structural parameters and cracks that evolve during the thermal processes.

[1] Ors, T., et al (2021) Mater. Sci. Eng. A-806, 140817
[2] Purushottam Raj Purohit, R.R.P., et al (2022) J. Appl. Cryst. 55, 737-750
[3] Gassenq A., et al, (2016) Appl. Phys. Lett. 108, 241902
[4] Hektor J., et al, (2018) Scripta Mater., 144, 1-4
[5] Ulrich, O., et al (2011) Rev. Sci. Instrum. 82, 033908
[6] Guinebretière, R., et al (2022) Phys. Rev. Mater. 6, 013602
[7] Purushottam Raj Purohit R.R.P.,et al, to be submitted in J. Appl. Cryst.