High resolution X ray diffraction infrastructure with uniaxial pressure

Author(s)

Vinícius Estevo Silva Frehse

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2022-11-25

Examining board members

Ricardo Donizeth dos Reis; Abner de Siervo; Flávia Regina Estrada

• Advisor: Cris Adriano; Ricardo Donizeth dos Reis; Guilherme de Andrade Calligaris

Abstract

Crystalline materials frequently have a relation between their macroscopic properties (resistivity, specific heat, magnetism) and their structure. Given that some materials are asymmetric in some directions, these properties can be correlated with the asymmetric crystalline arrangement (anisotropies). Therefore it is interesting to indirectly control said properties by modifying the dimensions of the material, specially the anisotropies. Thereby the development of an infrastructure that allows the deformation of preferential directions of materials while observing changes in their structure with X-Ray Diffraction (XRD) is described in this work. With that in mind, uniaxial strain cells made by Razorbill Instruments were compatibilized with the diffractometer setup as port of the commissioning of the EMA beamline in Sirius. To achieve that, a sample preparation and mounting routine was implemented, as to assure an ideal functioning of the cells. The selected samples were sapphire, for its high hardness, and \ce{Mn3Ge}, for the relation between its physical properties and its anisotropy. Beyond that, it was necessary to develop both a physical framework, to affix the cells on the diffractometer, and a virtual one, to control the strain generated by the cells. With the preparations concluded, the samples were deformed while there being made measurements of $\omega - 2\theta$, to observe changes in their lattice parameters, and Rocking Curves (RC), to analyze their rearrangements in mosaicity. In the case of sapphire , it was observed that the balance between the dimensions and the hardness of the sample are fundamental to guarantee a uniform pressure application. For \ce{Mn3Ge}, it was observed that there is a probable hysteresis in its compression and traction process. In addition, with this infrastructure deformations of ${\sim}0,18\%$ with a resolution of ${\sim}\SI{e-5}{\angstrom}$ can be achieved. Given the resolution obtained, three-dimensional Reciprocal Space Mappings (3D-RSM) were also generated, allowing the observation the volume around a reflection in the reciprocal space. From the development of this infrastructure it will be possible to relate the effect of deformations in anisotropic materials with their physical properties. Moreover the intention is to combine other techniques with XRD measurements, \eg transport measurements or magnetization, while also expanding the implementation to other types of materials, such as thin films (AU)

• FAPESP's process: 20/11399-5 - Uniaxial pressure tuning the symmetry of materials with non trivial topology
• Grantee: Vinícius Estevo Silva Frehse
• Support Opportunities: Scholarships in Brazil - Master