TY - JOUR

T1 - Topological Features of A+B2+[B5O9] Layered Pentaborates

T2 - Structural Changes in NaSr[B5O9] at High Temperatures or Why KCa[B5O9] Is Unstable?

AU - Volkov, Sergey N.

AU - Aksenov, Sergey M.

AU - Yukhno, Valentina A.

AU - Bubnova, Rimma S.

AU - Povolotskiy, Alexey V.

AU - Arsent'Ev, Maxim Yu

AU - Ugolkov, Valery L.

AU - Krzhizhanovskaya, Maria G.

N1 - Publisher Copyright: ©

PY - 2022/2/2

Y1 - 2022/2/2

N2 - Temperature-dependent structural investigations of layered pentaborate NaSr[B5O9] belonging to a family of compounds with the general formula A+B2+[B5O9] (A = Na, K; B = Ca, Sr, Ba, Pb) have been performed. The thermal expansion shows slightly anisotropic behavior (α11 = 7, α22 = 10, α33 = 22 × 10-6 °C1- at 100 °C) which is caused by preferential orientation of the pentaborate [B5O11] rigid groups (fundamental building units, FBUs) of the layer. The monoclinic β angle increases above 600 °C due to a heterovalent Sr2+ ↔ Na+ cation substitution. Members of the A+B2+[B5O9] family are represented by two structural types which are characterized by the different orientations of the pentaborate FBUs within the layers. A topological analysis of the layers has been made, and corresponding classifications of the cationic net are given. It was found that the type of the structure strongly depends on the difference in the ionic radii of alkaline A+ and alkaline-earth B2+ cations. Our ab initio calculations also indicate the KCa[B5O9] compound unstability. Based on the density functional theory (DFT) calculations, it was also shown that the compound KCa[B5O9] is unstable under ambient conditions. According to the geometry analysis, the reason for the instability is the K+ and Ca2+ cations are size mismatched.

AB - Temperature-dependent structural investigations of layered pentaborate NaSr[B5O9] belonging to a family of compounds with the general formula A+B2+[B5O9] (A = Na, K; B = Ca, Sr, Ba, Pb) have been performed. The thermal expansion shows slightly anisotropic behavior (α11 = 7, α22 = 10, α33 = 22 × 10-6 °C1- at 100 °C) which is caused by preferential orientation of the pentaborate [B5O11] rigid groups (fundamental building units, FBUs) of the layer. The monoclinic β angle increases above 600 °C due to a heterovalent Sr2+ ↔ Na+ cation substitution. Members of the A+B2+[B5O9] family are represented by two structural types which are characterized by the different orientations of the pentaborate FBUs within the layers. A topological analysis of the layers has been made, and corresponding classifications of the cationic net are given. It was found that the type of the structure strongly depends on the difference in the ionic radii of alkaline A+ and alkaline-earth B2+ cations. Our ab initio calculations also indicate the KCa[B5O9] compound unstability. Based on the density functional theory (DFT) calculations, it was also shown that the compound KCa[B5O9] is unstable under ambient conditions. According to the geometry analysis, the reason for the instability is the K+ and Ca2+ cations are size mismatched.

UR - http://www.scopus.com/inward/record.url?scp=85122677166&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/9af5f20c-1f4d-346e-9113-2ba6173eb46a/

U2 - 10.1021/acs.cgd.1c01031

DO - 10.1021/acs.cgd.1c01031

M3 - Article

AN - SCOPUS:85122677166

VL - 22

SP - 976

EP - 981

JO - Crystal Growth and Design

JF - Crystal Growth and Design

SN - 1528-7483

IS - 2

ER -