Temperature-dependent structural studies of mullite-type Bi2Fe4O9
Temperature-dependent structural studies of mullite-type Bi2Fe4O9
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DOI：
10.1016/j.jssc.2012.08.062
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发表时间：
2013-01
影响因子：
3.3
通讯作者：
M. Murshed;G. Nénert;M. Burianek;L. Robben;M. Mühlberg;H. Schneider;R. Fischer;T. Gesing
中科院分区：
文献类型：
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作者：
M. Murshed;G. Nénert;M. Burianek;L. Robben;M. Mühlberg;H. Schneider;R. Fischer;T. Gesing
本文报道了莫来石型Bi_2Fe_4O_9化合物随温度变化的结构研究。用粉末X射线衍射和单晶中子衍射测定了晶体结构。电池参数的热膨胀从最小到最大的顺序为a<c<B;根据所选区域，使用线性或非线性回归拟合它们的膨胀行为。各向异性的热膨胀监测相对于膨胀系数，各向异性因子，和多面体的几何形状。在900 K的各向异性因子的突变被观察到与斜率在BiO 6多面体体积。在相同温度下，FeO 4四面体畸变开始增加。用偏心率参数的绝对值探讨了Bi ~（3+）6s_2孤电子对的立体化学活性随温度的变化。该参数在773 K附近显示出显著下降。此外，还研究了粉末样品的平均晶粒尺寸和微观应变。观察到本征缺陷的愈合相对于减小的微应变，然后在约900 K以上进行晶体生长。在三个不同的区域中描述了温度相关的红外光谱。对370 cm − 1 ~ 1000 cm − 1的吸收特征进行去卷积需要9个拟合带，分解后的赝-Voigt元分别归属于Fe-O伸缩振动、Fe-O-Fe弯曲振动和O-Fe-O弯曲振动。所观察到的模式的移位相对于温度进行了描述。通过自相关分析确定了740 cm − 1和900 cm − 1之间的有效线宽参数Δcorr。Δcorr斜率在773 K附近的突变被解释为FeO 4四面体某些振动模式的变化。在773 K附近观察到的本征效应导致了在900 K附近发现的外参数变化。
We report on the temperature-dependent structural studies on the mullite-type Bi2Fe4O9compound. The crystal structures were determined using both powder X-ray diffraction and single crystal neutron diffraction. The thermal expansion of the cell parameters from smallest to largest occurred in the order a<c<b; their expansion behavior was fit using either linear or nonlinear regression according to the region of choice. The anisotropic thermal expansion was monitored with respect to the expansion coefficients, anisotropy factor, and polyhedral geometry. At 900K an abrupt change of the anisotropy factor is observed which correlates with a slope in the BiO6polyhedral volume. At the same temperature the FeO4tetrahedral distortion starts to increase. The temperature-dependent stereochemically activity of the Bi3+6s2lone electron pair was probed by the absolute value of eccentricity parameter. This parameter shows a significant drop at around 773K. Additionally, the average crystal size and micro-strain of the powder samples were studied. A healing of intrinsic defects is observed with respect to a decreasing micro-strain followed by crystal growth above about 900K. The temperature-dependent infrared spectra were described in three distinct zones. Deconvolution of the absorption features between 370cm−1and 1000cm−1required nine fitted bands, and the decomposed Pseudo-Voigt elements were assigned to Fe–O stretching, Fe–O–Fe bending and O–Fe–O bending vibrations. The shift of the observed modes was described with respect to temperature. An effective linewidth parameter Δcorr was determined by autocorrelation analysis between 740cm−1and 900cm−1for each temperature-dependent spectrum. The break of the slope of Δcorr at about 773K was interpreted as the change of some vibrational modes of the FeO4tetrahedra. The intrinsic effects observed around 773K are responsible for extrinsic parameter changes found around 900K.