2468 KB68 KB199820252022Makovec, Darkoštevilka:4letnik:69str. 756-771DOI:10.17344/acsi.2022.7775COBISSID_HOST:141459459ISSN:1580-3155URN:URN:NBN:SI:doc-0T71CEZHenSlovensko kemijsko društvoActa chimica slovenicaAurivillius structurecrystal structurehexaferriteskristalna strukturalayered perovskitesNanodelcinanoparticlesPerovskitPolimorfizem (kristalografija)polymorphismsAdaptation of the crystal structure to the confined size of mixed-oxide nanoparticles|Chemical composition and crystal structure are central to defining the functional properties of materials. But when a material is prepared in the form of nanoparticles, the structure and, as a consequence, the composition will also frequently change. Understanding these changes in the crystal structure at the nanoscale is therefore essential not only for expanding fundamental knowledge, but also for designing novel nanostructures for diverse technological and medical applications. The changes can originate from two thermodynamically driven phenomena: (i) a crystal structure will adapt to the restricted size of the nanoparticles, and (ii) metastable structural polymorphs that form during the synthesis due to a lower nucleation barrier (compared to the equilibrium phase) can be stabilized at the nanoscale. The changes to the crystal structure at the nanoscale are especially pronounced for inorganic materials with a complex structure and composition, such as mixed oxides with a structure built from alternating layers of several structural blocks. In this article the complex structure of nanoparticles will be presented based on two examples of well-known and technologically important materials with layered structures: magnetic hexaferrites (BaFe12O19 and SrFe12O19) and ferroelectric Aurivillius layered-perovskite bismuth titanate (Bi4Ti3O12)Uporabne lastnosti materialov so v veliki meri določene s sestavo in kristalno strukturo materialov. Struktura materiala in posledično tudi njegova sestava se lahko znatno spremenita, če material pripravimo v obliki nanodelcev. Poznavanje sprememb v kristalni strukturi zaradi končne dimenzije nanomaterialov je torej pomembno tako s stališča širjenja osnovnega znanja, kot tudi za načrtovanje novih nanomaterialov za uporabo v tehnologiji in medicini. Spremembe v strukturi so lahko posledica dveh različnih pojavov: (i) kristalna struktura se prilagodi končni velikosti nanodelcev, in (ii) z majhno velikostjo delcev lahko stabiliziramo različne metastabilne strukturne polimorfe, ki nastanejo med sintezo v tekočem zaradi nižje energijske pregrade za nukleacijo v primerjavi z energijsko pregrado potrebno za nukleacijo ravnotežnih faz. Omenjene spremembe v kristalni strukturi so posebej pogoste pri anorganskih materialih s kompleksno strukturo in sestavo, kot so zmesni oksidi s plastovito strukturi sestavljeno iz več strukturnih blokov. Pričujoči članek pojasnjuje kompleksno strukturo nanodelcev na primerih dveh dobro znanih in tehnološko zelo pomembnih materialov s plastovito strukturo: magnetnih heksaferitov (BaFe12O19 in SrFe12O19) in feroelektričnega bizmutovega titanata (Bi4Ti3O12) s plastovito perovskitno strukturo Aurivilliusovega tipaTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaSlovensko kemijsko društvo