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Tailoring structural properties of lanthanum orthoniobates through an isovalent substitution on the Nb-site
Inorganic Chemistry Frontiers ( IF 7 ) Pub Date : 2018-07-02 00:00:00 , DOI: 10.1039/c8qi00524a
Sebastian Wachowski 1, 2, 3, 4, 5 , Bartosz Kamecki 1, 2, 3, 4, 5 , Piotr Winiarz 1, 2, 3, 4, 5 , Kacper Dzierzgowski 1, 2, 3, 4, 5 , Aleksandra Mielewczyk-Gryń 1, 2, 3, 4, 5 , Maria Gazda 1, 2, 3, 4, 5
Affiliation  

A tetragonal polymorph of lanthanum orthoniobate can be stabilized to room temperature by the substitution of Nb with an isovalent element. LaNb1−xAsxO4 (0 < x ≤ 0.3), where As is an element stabilizing the tetragonal structure, were successfully synthesized using a combined co-precipitation and solid-state reaction method. The phase transition temperature, above which the material has a tetragonal structure, decreases linearly with increasing As content, and LaNb0.7As0.3O4 is tetragonal at room temperature. The analysis of the influence of different isovalent substituents, namely V, Sb and Ta, has shown that there is a relation between the properties of the chemical element and its effect on the structure. It was proposed that the electronegativity of the substituent determines the type of stabilization – the tetragonal/monoclinic structure is stabilized by chemical elements with electronegativity higher/lower than that of niobium. The slope of the phase transition temperature dependence on the substituent content has been proposed as a parameter determining the “quality” of the stabilization, since a steeper function leads to a larger decrease of transition temperature for the same content of different substituents. The analysis has shown that apart from the electronegativity, the stabilization of the tetragonal structure depends also on the ionic radius of a substituent. Arsenic has been found to be a better stabilizer of the tetragonal polymorph of lanthanum orthoniobate than Sb, but worse than V.

中文翻译:

通过在Nb位上进行等价取代来调整邻苯二甲酸镧镧的结构性质

通过用等价元素取代Nb,可以将原铌酸镧的四边形多晶型物稳定在室温下。LANB 1- X作为X Ø 4(0 < X ≤0.3),其中,由于是稳定四方结构的元件,使用组合的共沉淀和固态反应方法成功地合成。材料具有四方结构的相变温度随As含量的增加和LaNb 0.7 As 0.3 O 4的增加而线性降低。在室温下呈四边形。对不同的等价取代基(即V,Sb和Ta)的影响的分析表明,化学元素的性质与其对结构的影响之间存在联系。有人提出,取代基的电负性决定了稳定化的类型–四方/单斜晶结构被电负性比铌高/低的化学元素稳定。已经提出相变温度依赖于取代基含量的斜率作为确定稳定性的“质量”的参数,因为对于不同取代基的相同含量,较陡的函数导致转变温度的较大降低。分析表明,除了电负性,四方结构的稳定性还取决于取代基的离子半径。已发现砷是原铌酸镧四方晶型更好的稳定剂,但比钒差。
更新日期:2018-07-02
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