X-ray diffraction studies of epoxy-based composites with various BiFeO3 particles

X-ray diffraction tests (D8 Advance, Bruker AXS) were performed on epoxy composites containing two BiFeO3 powders with different grain sizes - submicrometric (sBFO) and micrometric (mBFO). The tests were carried out under tensile and compression conditions. In addition, for tests under compression conditions, an analysis of residual stresses in all composites was performed, using the peak (514) of the R3c structure, characteristic of 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°.

本研究针对两种不同晶粒尺寸的铁酸铋（BiFeO3）粉末掺杂的环氧树脂复合材料开展X射线衍射（X-ray diffraction, XRD）测试，所用粉末分别为亚微米级（sBFO）与微米级（mBFO）铁酸铋，测试设备为D8 Advance衍射仪（布鲁克AXS，Bruker AXS）。测试工况涵盖拉伸与压缩两种模式。此外，针对压缩工况下的试样，采用铁酸铋R3c结构特征的（514）晶面衍射峰，对所有复合材料的残余应力开展了分析。

本研究使用德国卡尔斯鲁厄布鲁克AXS公司生产的D8 Advance衍射仪，配置Cu-Kα射线靶（波长λ=1.54 Å），工作参数为电压40 kV、电流40 mA，分别对粉末样品与复合材料进行XRD表征。其中粉末样品的扫描范围为10°~140° 2θ，扫描速率0.30°/min，步长0.01°；复合材料试样则采用2°/min的扫描速率，步长同样为0.01°。数据采集采用德国卡尔斯鲁厄布鲁克AXS公司生产的LYNXEYE XE-T线型探测器，工作于改进型高分辨模式。为抑制铁酸铋结构中铁离子引发的荧光背景干扰，将探测器的高阈值甄别器维持在0.954 V，同时将低阈值甄别器从0.614 V提升至0.750 V。

残余应力XRD分析依据EN-15305标准开展，采用D8 Advance衍射仪的等倾斜测试模式，以铁酸铋相的（514）晶面衍射峰为分析对象，该峰在2θ衍射图谱中的标称位置为132.429°。残余应力分析所用材料参数如下：泊松比0.2695，杨氏模量143.53 GPa[4,5]，由此计算得到S₁ = -1.878 × 10⁻⁶ MPa⁻¹，1/S₂ = 8.845 × 10⁻⁶ MPa⁻¹。以11.6 MPa作为无应力材料的基准值。应力分析过程中，针对（514）晶面衍射峰位采用标准拟合方法，并将应力加载模式设定为法向。

压缩测试采用安装于D8 Advance衍射仪上的DEBEN微拉伸加载台，配备2 kN载荷上限的十字头加载机构，加载速率为0.4 mm/min，最大施加应力达20 MPa，测试扫描参数为扫描速率2°/min，步长0.01°。