X-ray diffraction studies of BiFeO3 powders characterized by different particle size - submicrometric (sBFO) and micrometric (mBFO), including residual stress analysis in powders, determined by sin2(psi) method using (514) peak of rhombohedral R3c structure typical for BiFeO3.
XRD studies were performed on powder samples and composites using the D8 Advance diffractometer (Bruker AXS, Karlsruhe, Germany) with Cu-Kα cathode (λ=1.54 Å) operating at 40 kV voltage and 40 mA current. The scan rate was 0.30°/min with scanning step 0.01° in range of 10° to 140° 2Θ for powder, while for composites scan rate 2°/min with scanning step 0.01° was applied. Data collection was performed using LYNXEYE XE-T linear detector (Bruker AXS, Karlsruhe, Germany), operating in a modified high-resolution mode. The high threshold discriminator was maintained at 0.954 V level, while the lower threshold discriminator of detector was increased from 0.614 V up to 0.750 V, in order to minimize fluorescence, regarding the presence of iron ions in the BiFeO3 structure.
Stress-XRD analysis was performed with use of iso-inclination mode of D8 Advance (Bruker AXS, Karlsruhe, Germany) based on (514) peak of BiFeO3 phase with the nominal position at 132.429° of 2θ pattern respectively, according to EN-15305 standard. For residual stress analysis, the following materials parameters were used: Poisson ratio 0.2695 and Young modulus 143.53 GPa4,5, which gives S1 = -1.878 ∙ 10-6 MPa and 1/S2 = 8.845 ∙ 10-6 MPa-1. The 11.6 MPa limit was used for a stress-free material. For stress analysis, the standard-fit was used in (514) peak position fitting. Applied stress mode was established as normal. For compressive tests, the DEBEN microtensile stage mounted at D8 Advance diffractometer with a 2kN crosshead was used, moving with a speed of 0.4 mm/min. Studies were performed up to 20 MPa applied stress, using scan rate 2°/min with scanning step 0.01°.
