CAJ | 학술논문

近年来,实验发现钛酸铅基材料具有负热膨胀性,且其热膨胀程度会受到掺杂元素的影响。目前所研究的A位掺杂体系中,仅Cd原子掺杂能使钛酸铅负热膨胀性增强。所以研究A位掺杂钛酸铅,比较Cd原子与其他原子在掺杂钛酸铅时化学键的异同,有助于深刻理解钛酸铅负热膨胀的本质。本文利用第一性原理,分别优化了Sr、Ba、Cd掺杂钛酸铅的晶格常数,计算了它们的态密度和电荷密度。结果表明Cd-O键的共价性强于Pb-O键,而Ba-O键和Sr-O键几乎呈离子性, Ba/Sr对Pb的替代削弱了化合物的共价性,降低了自发极化强度。与实验测量的热膨胀系数对比可以发现,A位原子与氧原子之间的共价性增强,化合物负热膨胀程度升高；若A位原子与氧原子之间的共价性削弱,负热膨胀程度降低。可见A位原子与氧原子之间的共价性影响了钛酸铅基化合物负热膨胀性。
근년래,실험발현태산연기재료구유부열팽창성,차기열팽창정도회수도참잡원소적영향。목전소연구적A위참잡체계중,부Cd원자참잡능사태산연부열팽창성증강。소이연구A위참잡태산연,비교Cd원자여기타원자재참잡태산연시화학건적이동,유조우심각리해태산연부열팽창적본질。본문이용제일성원리,분별우화료Sr、Ba、Cd참잡태산연적정격상수,계산료타문적태밀도화전하밀도。결과표명Cd-O건적공개성강우Pb-O건,이Ba-O건화Sr-O건궤호정리자성, Ba/Sr대Pb적체대삭약료화합물적공개성,강저료자발겁화강도。여실험측량적열팽창계수대비가이발현,A위원자여양원자지간적공개성증강,화합물부열팽창정도승고；약A위원자여양원자지간적공개성삭약,부열팽창정도강저。가견A위원자여양원자지간적공개성영향료태산연기화합물부열팽창성。
Recent experimental results have indicated that the negative thermal expansion is a common phenomenon in PbTiO3-based materials, and that this expansion is affected by various substitutions. Interestingly, Cd substitution in PbTiO3 has a unique effect compared with other A-site substitutions, in that it enhances negative thermal expansion. Therefore, studying A-site substitution in PbTiO3, the role of which still remains unclear, would provide a deeper understanding of the nature of the negative thermal expansion of PbTiO3-based materials. Herein we report the results of structural calculations, densities of states and the minimum electron densities of Pb1-xSrxTiO3, Pb1-xBaxTiO3, and Pb1-xCdxTiO3 supercells on the basis of chemical bond first-principles calculations. The results demonstrate that the hybridization between Cd-O orbitals is more pronounced than that between Pb-O orbitals, while the bonding between Ba/Sr and O is almost ionic in nature. Cd substitution was found to have an unusual effect in terms of enhancing the average bulk coefficient of thermal expansion in PbTiO3. In contrast, Ba and Sr substitutions reduce the coefficient. Thus, the covalency in the bonding between the A-site and O in PbTiO3-based materials is responsible for the enhanced negative thermal expansion.