Crystal-chemistry of mullite-type aluminoborates Al18B4O33 and Al5BO9: A stoichiometry puzzle

Thermal Expansion of Aluminoborates

“…Data were collected with o-j-scans and subsequently treated using Apex2 v. 2009-11.0 software package (Bruker 2009). The structural model by Fisch et al (2011) was used for refinement of Al 5 BO 9 data whereas grandidierite and jeremejevite structures were solved by direct methods. Details of single-crystal XRD data treatment are given in Table 1.…”

“…Details of single-crystal XRD data treatment are given in Table 1. Atomic coordinates and anisotropic displacement parameters are listed in Fisch (2011).…”

Boron mullite: Formation and basic characterization

“…The Al 2 O 3 -rich aluminoborate is reported having two slightly different chemical compositions: Al 5 BO 9 and Al 18 B 4 O 33 . The result of recent crystal chemical investigations by Fisch et al [4] yielded a stoichiometry close to Al 5 BO 9 , assuming that the Al 18 B 4 O 33 composition might be the result of inaccurate chemical analyses.…”

Characterization of the glass-to-vitroceramic transition in yttrium aluminum borate laser glasses using solid state NMR

“…The foregoing data are important in connection to a current on-going discussion regarding a discrepancy between the crystal structure and the exact chemical composition of this compound, suggesting the presence of some structural disorder [36][37][38]. Chemical analyses have repeatedly suggested a composition of Al 18 B 4 O 33 (Al 4.91 B 1.09 O 9 ), whereas the structural data derived from single-crystal X-ray diffraction studies (mullite structure) are consistent with the nominal formula Al 5 BO 9 [21].…”

“…Recently the question about the correct chemical stoichiometry of this compound has been addressed comprehensively by Fisch et al [38], on the basis of combined single-crystal diffraction and chemical analysis data. The authors concluded that the correct stoichiometry is somehow in between Al 18 B 4 O 33 and Al 5 BO 9 and they attributed the deviation from Al 5 BO 9 composition to a very low amount of Al vacancies at a five-fold coordinated site, which is charge balanced by an additional nearby three-fold coordinated B site [38]. Using solid state NMR, the authors were unable to detect B(4) units.…”