TY - JOUR

T1 - The structural role and coordination environment of cobalt in 45P2O5-CaO-Na2O phosphate glasses: thermal properties and Raman, UV-vis-NIR, and EPR spectroscopy

AU - Avila Salazar, Dahiana A

AU - Fedin, Matvey

AU - Hartramph, Wolfram

AU - Brauer, Delia S

N1 - The authors acknowledge funding by the German Research Foundation (DFG; grant BR 4608/4) which made this research possible. D. A. A. S. acknowledges funding by the Johan Gadolin Program for her research stay at Åbo Akademi, Turku, Finland. M. F. thanks MSHE (Grant No. 075-15-2020-779). The authors wish to thank Prof. Lothar Wondraczek and Omar Benzine (University of Jena) for UV-vis-NIR and Raman analyses, Yuki Oi (Nagoya Institute of Technology, Japan) for his assistance in preparing ICP-OES samples, Jaana Paananen for HSM and Peter Backman for DSC/TGA-MS measurements (both Åbo Akademi, Finland) and Dr Gavin Mountjoy (University of Kent, UK) and Dmitrii Bogdanov (Saint Petersburg State University) for fruitful discussions.

PY - 2023/4/4

Y1 - 2023/4/4

N2 - Cobalt-containing materials are of interest for a wide range of applications, from biomaterials to solid-state lasers in optics. For instance, Co2+ is known to trigger the formation of new blood vessels, i.e. angiogenesis. Here, the use of phosphate glasses as a vehicle for local release of Co2+ ions is an attractive strategy to overcome the vascularisation limitation in tissue engineering. This study aimed to establish structure-property correlations as a function of the coordination environment of cobalt in 45P2O5-(30 - x)CaO-25Na2O-xCoO (x: 0.01 to 10 mol%) glasses. Constant polymerization and O/P ratio, resulting ultimately in constant basicity, were shown by ICP-OES and Raman spectroscopy. The latter, combined with EPR analysis, indicated that Co2+ was the predominant oxidation state and the presence of Co3+ can be excluded. UV-vis-NIR absorption spectra showed that the ratio between Co2+ in four- and six-fold coordination remained constant throughout the glass series. Their thermal properties measured by DSC and heating microscopy did not change much in the substitution range studied here. The steady trend in Tg values suggests a compensation between two opposite effects caused by the presence of four and six-fold coordinated Co2+, both being present at a constant ratio throughout the glasses. Accordingly, the higher field strength of Co2+ compared to that of Ca2+ is expected to strengthen the glass network. In contrast, four-fold coordinated cobalt is expected to weaken the network by connecting fewer fragments of the phosphate glass network than six-fold coordinated cobalt. These results indicate that the structural properties of the glasses with constant basicity are influenced by the coordination number of Co2+.

AB - Cobalt-containing materials are of interest for a wide range of applications, from biomaterials to solid-state lasers in optics. For instance, Co2+ is known to trigger the formation of new blood vessels, i.e. angiogenesis. Here, the use of phosphate glasses as a vehicle for local release of Co2+ ions is an attractive strategy to overcome the vascularisation limitation in tissue engineering. This study aimed to establish structure-property correlations as a function of the coordination environment of cobalt in 45P2O5-(30 - x)CaO-25Na2O-xCoO (x: 0.01 to 10 mol%) glasses. Constant polymerization and O/P ratio, resulting ultimately in constant basicity, were shown by ICP-OES and Raman spectroscopy. The latter, combined with EPR analysis, indicated that Co2+ was the predominant oxidation state and the presence of Co3+ can be excluded. UV-vis-NIR absorption spectra showed that the ratio between Co2+ in four- and six-fold coordination remained constant throughout the glass series. Their thermal properties measured by DSC and heating microscopy did not change much in the substitution range studied here. The steady trend in Tg values suggests a compensation between two opposite effects caused by the presence of four and six-fold coordinated Co2+, both being present at a constant ratio throughout the glasses. Accordingly, the higher field strength of Co2+ compared to that of Ca2+ is expected to strengthen the glass network. In contrast, four-fold coordinated cobalt is expected to weaken the network by connecting fewer fragments of the phosphate glass network than six-fold coordinated cobalt. These results indicate that the structural properties of the glasses with constant basicity are influenced by the coordination number of Co2+.

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85151035951&origin=inward&txGid=b9bc0eee8f1c52839039835a7f78b3b7

UR - https://www.mendeley.com/catalogue/0f7e2703-8128-3049-b31f-b27fd6ab01df/

U2 - 10.1039/d3dt00279a

DO - 10.1039/d3dt00279a

M3 - Article

C2 - 36920418

VL - 52

SP - 4526

EP - 4536

JO - Dalton Transactions

JF - Dalton Transactions

SN - 1477-9226

IS - 14

ER -