Issue 32, 2022

Solid solutions based on BaZn2Si2O7 with thermal expansions from negative to highly positive – a review

Abstract

The compound BaZn2Si2O7 shows a transition from a monoclinic low temperature phase to an orthorhombic high temperature phase at 280 °C which is accompanied by an increase in the volume of 3.3%. The temperature of the phase transition can be shifted to higher temperature by a replacement of Zn2+ by Mg2+ or the divalent transition metal cations, Mn2+, Co2+, Ni2+ or Cu2+ as well as by the replacement of Si4+ by Ge4+. By contrast, the replacement of Ba2+ by Sr2+ leads to the shift of the phase transition to lower temperatures. The coefficient of thermal expansion of the low temperature phase is exceptionally high and in the range from 10 to 15 10−6 K−1, while that of the high temperature phase is small or even negative. The reason of the latter effect is a rotation of bridged ZnO4 tetrahedra in opposite directions. This results in a strongly negative thermal expansion of the b-axis, while the expansion of the a- and c-axes are positive. Although melts of the stoichiometric compounds do not build a continuous network, glass formation can be achieved by the addition nucleation inhibitors, such as ZrO2, Al2O3 or La2O3 or an excess of SiO2. The quenched glasses crystallize at the surface while bulk crystallization is not observed. This changes if noble metals or higher concentrations of ZrO2, WO3 or P2O5 are added to the glass, then also bulk crystallization is possible. Homogeneously crystallized glass ceramics can also be obtained, by sinter crystallization of powdered glass or using sol–gel derived crystalline powders. Adjusting the composition of the respective solid solutions enables to tailor the coefficient of thermal expansion from negative to highly positive values.

Graphical abstract: Solid solutions based on BaZn2Si2O7 with thermal expansions from negative to highly positive – a review

Article information

Article type
Highlight
Submitted
16 Mei 2022
Accepted
18 Jul 2022
First published
18 Jul 2022
This article is Open Access
Creative Commons BY license

CrystEngComm, 2022,24, 5663-5674

Solid solutions based on BaZn2Si2O7 with thermal expansions from negative to highly positive – a review

C. Thieme and C. Rüssel, CrystEngComm, 2022, 24, 5663 DOI: 10.1039/D2CE00667G

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