TY - JOUR

T1 - A structural origin of both positive and negative thermal expansion in langbeinite-, arcanite- and metathenardite-type and related Rb2SO4 and Rb2Ca2(SO4)3 compounds

AU - Шаблинский, Андрей Павлович

AU - Демина, Софья Владимировна

AU - Бирюков, Ярослав

AU - Бубнова, Римма Сергеевна

AU - Кржижановская, Мария Георгиевна

AU - Филатов, Станислав Константинович

PY - 2025/11

Y1 - 2025/11

N2 - In this work a nature of an anisotropy of positive and negative thermal expansion of langbeinite-, arcanite- and metathenardite-type compounds is explained in terms of crystal structure data. The linear αL thermal expansion coefficient for the langbeinite and arcanite-type compounds varies from 11 to −15 and 71 to −10 ∙10−6 °С−1, respectively, while the metathenardite ones expand almost positively and negatively only along the a axis (αa = −14 ∙ 10−6 °С−1 in the range 475–600 °C). Thermal expansion of Rb2SO4 and langbeinite-type Rb2Ca2(SO4)3 is investigated by high-temperature powder X-ray diffraction in temperature ranges 25–900 and 25–1000 °C, respectively. A temperature-induced structural phase transition Pmcn↔P63/mmc (or β– ↔ α–Rb2SO4) is observed at 663 ± 12 °C. Crystal structure of the high-temperature α–Rb2SO4 was refined at 700 and 1000 °C. Thermal expansion of Rb2SO4 is highly anisotropic: αa = 35.9(1), αb = 28.9(2), αc = 70(1)∙10−6 °С−1 for β–Rb2SO4 (at 300 °C); αa = 55(5), αc = 115(9)∙10−6 °С−1 for α–Rb2SO4 (at 800 °C). The anisotropy of the expansion of both Rb2SO4 modifications is explained by a rotation of the SO4 tetrahedra. Crystal structure of the langbeinite-type Rb2Ca2(SO4)3 is described in terms of M(TO4)6 microblocks. Calculated αa thermal expansion coefficient for Rb2Ca2(SO4)3 is equal to 10.4(2) ∙ 10−6 °С−1 (at 25 °C). Main structural mechanisms of the expansion of Rb2Ca2(SO4)3 are “rocking” polyhedra and hinge deformation of the M(TO4)6 microblocks.

AB - In this work a nature of an anisotropy of positive and negative thermal expansion of langbeinite-, arcanite- and metathenardite-type compounds is explained in terms of crystal structure data. The linear αL thermal expansion coefficient for the langbeinite and arcanite-type compounds varies from 11 to −15 and 71 to −10 ∙10−6 °С−1, respectively, while the metathenardite ones expand almost positively and negatively only along the a axis (αa = −14 ∙ 10−6 °С−1 in the range 475–600 °C). Thermal expansion of Rb2SO4 and langbeinite-type Rb2Ca2(SO4)3 is investigated by high-temperature powder X-ray diffraction in temperature ranges 25–900 and 25–1000 °C, respectively. A temperature-induced structural phase transition Pmcn↔P63/mmc (or β– ↔ α–Rb2SO4) is observed at 663 ± 12 °C. Crystal structure of the high-temperature α–Rb2SO4 was refined at 700 and 1000 °C. Thermal expansion of Rb2SO4 is highly anisotropic: αa = 35.9(1), αb = 28.9(2), αc = 70(1)∙10−6 °С−1 for β–Rb2SO4 (at 300 °C); αa = 55(5), αc = 115(9)∙10−6 °С−1 for α–Rb2SO4 (at 800 °C). The anisotropy of the expansion of both Rb2SO4 modifications is explained by a rotation of the SO4 tetrahedra. Crystal structure of the langbeinite-type Rb2Ca2(SO4)3 is described in terms of M(TO4)6 microblocks. Calculated αa thermal expansion coefficient for Rb2Ca2(SO4)3 is equal to 10.4(2) ∙ 10−6 °С−1 (at 25 °C). Main structural mechanisms of the expansion of Rb2Ca2(SO4)3 are “rocking” polyhedra and hinge deformation of the M(TO4)6 microblocks.

KW - Arcanite

KW - Crystal structure

KW - Langbeinite

KW - Metathenardite

KW - Negative thermal expansion

KW - Rubidium sulphate

KW - Thermal expansion

UR - https://www.mendeley.com/catalogue/b4460e1f-853d-3e36-b309-6371df9fffe6/

U2 - 10.1016/j.ceramint.2025.08.360

DO - 10.1016/j.ceramint.2025.08.360

M3 - Article

VL - 51

SP - 51342

EP - 51350

JO - Ceramics International

JF - Ceramics International

SN - 0272-8842

IS - 26-C

ER -