title: Ba(1-x)Sr(x)Zn2Si2O7--A new family of materials with negative and very high thermal expansion.
abstract: The compound BaZn2Si2O7 shows a high coefficient of thermal expansion up to a temperature of 280 °C, then a transition to a high temperature phase is observed. This high temperature phase exhibits negative thermal expansion. If Ba(2+) is successively replaced by Sr(2+), a new phase with a structure, similar to that of the high temperature phase of BaZn2Si2O7, forms. At the composition Ba0.8Sr0.2Zn2Si2O7, this new phase is completely stabilized. The crystal structure was determined with single crystal X-ray diffraction using the composition Ba0.6Sr0.4Zn2Si2O7, which crystallizes in the orthorhombic space group Cmcm. The negative thermal expansion is a result of motions and distortions inside the crystal lattice, especially inside the chains of ZnO4 tetrahedra. Dilatometry and high temperature X-ray powder diffraction were used to verify the negative thermal expansion. Coefficients of thermal expansion partially smaller than -10·10(-6) K(-1) were measured.
authors.affiliation: Chair of Glass Chemistry I, Jena University, Fraunhoferstr. 6, 07743 Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Thieme
authors.affiliation: Institute of Inorganic and Analytical Chemistry, Jena University, Lessingstr. 8, 07743 Jena, Germany.
authors.forename: Helmar
authors.initials: H
authors.lastname: Görls
authors.affiliation: Chair of Glass Chemistry I, Jena University, Fraunhoferstr. 6, 07743 Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Rüssel