Sol–gel powder synthesis and preparation of ceramics with high- and low-temperature polymorphs of Ba Sr1-Zn2Si2O7 (x= 1 and 0.5): A novel approach to obtain zero thermal expansion

ACS Appl. Mater. Interfaces

Schlesier

Bocker

et al. 2016

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The thermal expansion behavior of sintered glass-ceramics containing high concentrations of Ba1-xSrxZn2Si2O7, a phase with very low and highly anisotropic thermal expansion behavior, was investigated. The observed phase has the crystal structure of the high-temperature phase of BaZn2Si2O7, which can be stabilized by the introduction of Sr(2+) into this phase. The high anisotropy leads to microcracking within the volume of the samples, which strongly affects the dilatometric thermal expansion. However, these cracks also have an influence on the nominal thermal expansion of the as-mentioned phase, which decreases if the cracks appear. Below a grain size of approximately 80 μm, the sintered glass-ceramics have almost no cracks and show positive thermal expansion. Hence, coefficients of thermal expansion between -5.6 and 6.5 × 10(-6) K(-1) were measured. In addition to dilatometric studies, the effect of the microstructure on the thermal expansion was also measured using in situ X-ray diffraction at temperatures up to 1000 °C.

Section: Discussionsupporting

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Thermal Expansion of Sintered Glass Ceramics in the System BaO–SrO–ZnO–SiO₂ and Its Dependence on Particle Size

ACS Appl. Mater. Interfaces

Schlesier

Bocker

et al. 2016

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“…This should make such materials extremely resistant to thermal shock. However, obtaining a densely sintered material from such a highly anisotropic phase needs special techniques, such as sol-gel synthesis, in order to get crack-free materials [ 13 ]. If the Ge-concentration gets too high, the LT-modification becomes stabilized.…”

Section: Resultsmentioning

confidence: 99%

Negative Thermal Expansion in Ba0.5Sr0.5Zn2SiGeO7

2016

Materials

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Solid solutions with the composition Ba0.5Sr0.5Zn2Si2-xGexO7 and BaZn2Si2-xGexO7 were prepared with different values of x using a conventional mixed oxide route. Both compounds exhibit very different thermal expansion, which is due to the different crystal structures. Ba0.5Sr0.5Zn2Si2-xGexO7 solid solutions exhibit the structure of high-temperature BaZn2Si2O7 and show negative thermal expansion, which was proven via high-temperature X-ray diffraction. Up to around x = 1, the crystal structure remains the same. Above this value, the low-temperature phase becomes stable. The Sr-free solid solutions have the crystal structure of low-temperature BaZn2Si2O7 and show also a limited solubility of Ge. These Sr-free compositions show transitions of low- to high-temperature phases, which are shifted to higher temperatures with increasing Ge-concentration.

“…9 This enables the preparation of materials with a low thermal expansion. 10 Such materials, however, based on lithium aluminosilicates and not on Ba 1−x Sr x Zn 2 Si 2 O 7 , are nowadays used for a large variety of applications, such as cook top panels, telescope mirrors, furnace windows and various optical devices. [11][12][13] Negative thermal expansion at room temperature and higher is an uncommon physical property, since most materials expand with increasing temperature.…”

Section: Introductionmentioning

confidence: 99%

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

Rüssel²

2022

CrystEngComm

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