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Effects of Ca 2+ , Mg 2+ , Na + , and K + substitutions on the microstructure and electrical properties of GdCoO 3 ceramics
Journal of Electroceramics ( IF 1.7 ) Pub Date : 2020-12-30 , DOI: 10.1007/s10832-020-00226-3
Sea-Fue Wang , Yung-Fu Hsu , Yi-Le Liao , Tung Lin , Piotr Jasinski

GdCoO3-δ, Gd0.975Na0.025CoO3-δ, Gd0.98K0.02CoO3-δ, Gd0.98Ca0.02CoO3-δ, and GdCo0.99Mg0.01O3-δ ceramics were prepared via a solid-state reaction route. Among the dopants studied, substitution with Ca2+ slightly enhanced the densfication of GdCoO3 ceramics. All the lattice parameters of the doped ceramics were larger than those of pure GdCoO3-δ ceramic (a = 5.223 Å, b = 5.389 Å and c = 7.451 Å), and their cell volumes increased by 0.30% to 1.40% because the substitution ions were larger in size. X-ray diffraction and scanning electron microscopy results indicate that no second phase is present. The average grain size of the GdCoO3 ceramics (7.6 μm) slightly increased by the Na+, K+ and Mg2+ substitutions and decreased by the Ca2+ substitution. In all cases, the intergranular fracture surfaces revealed the presence of trapped pores due to rapid grain growth. The oxidation states and percentages of Co ions were determined from the Co 2p X-ray photoelectron spectra. Na+, K+, Ca2+, and Mg2+ substitution in the GdCoO3-δ ceramic resulted in slight oxidation of the Co ions accompanied by a decrease in oxygen vacancies. After porosity correction using the Bruggeman effective medium approximation, Gd0.98Ca0.02CoO3-δ had the largest electrical conductivity at all measured temperatures among the compositions studied, which was 144% higher at 500 °C and 16% higher at 800 °C compared to those of GdCoO3-δ ceramic (500 °C: 133.3 S·cm−1; 800 °C: 692.4 S·cm−1). The substantial increase in the electrical conductivity of the doped GdCoO3-δ ceramics is due to the electronic compensation of acceptor doping, \( {\mathrm{N}a}_{Gd}^{"} \), \( {K}_{Gd}^{"} \), and \( {Ca}_{Gd}^{\prime } \), which resulted in the formation of hole carriers and the elimination of oxygen vacancies (\( {V}_o^{\bullet \bullet } \)), which generated additional Co4+ (\( {Co}_{Co}^{\bullet } \)).



中文翻译:

Ca 2+,Mg 2+,Na +和K +取代对GdCoO 3陶瓷的微观结构和电性能的影响

通过固相反应制备GdCoO 3- δ,Gd 0.975 Na 0.025 CoO 3- δ,Gd 0.98 K 0.02 CoO 3- δ,Gd 0.98 Ca 0.02 CoO 3- δ和GdCo 0.99 Mg 0.01 O 3- δ陶瓷路线。在研究的掺杂剂中,用Ca 2+取代会稍微增强GdCoO 3陶瓷的致密化。掺杂陶瓷的所有晶格参数都大于纯GdCoO 3- δ的晶格参数陶瓷(a  = 5.223Å,b  = 5.389Å,c  = 7.451Å),并且由于取代离子的尺寸较大,它们的晶胞体积增加了0.30%至1.40%。X射线衍射和扫描电子显微镜结果表明不存在第二相。通过Na +,K +和Mg 2+取代,GdCoO 3陶瓷的平均晶粒尺寸(7.6μm )略有增加,而通过Ca 2+取代则降低了。在所有情况下,由于晶粒的快速生长,晶间断裂表面均显示出存在被捕获的孔隙。由Co 2p X射线光电子能谱确定Co离子的氧化态和百分比。娜GdCoO 3- δ陶瓷中的+,K +,Ca 2+和Mg 2+取代导致Co离子轻微氧化,同时氧空位降低。使用Bruggeman有效介质近似法对孔隙度进行校正后,在所有测得温度下,Gd 0.98 Ca 0.02 CoO 3- δ在所有测得的成分中均具有最大的电导率,与500°C相比高144%,在800°C时高16%那些GdCoO的3- δ陶瓷(500℃:133.3 S·厘米-1 ; 800℃:692.4 S·厘米-1)。掺杂的GdCoO3 陶瓷电导率的显着提高是由于受主掺杂的电子补偿\({\ mathrm {N} a} _ {Gd} ^ {“} \)\({K } _ {Gd} ^ {“} \)\({Ca} _ {Gd} ^ {\ prime} \),从而形成了空穴载流子并消除了氧空位(\({V} _o ^ {\ bullet \ bullet} \)),生成额外的Co 4+\({Co} _ {Co} ^ {\ bullet} \))。

更新日期:2020-12-31
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