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Characterization of the thermal expansion in the rare earth di-titanates is important for their use in high-temperature structural and dielectric applications. Powder samples of the rare earth di-titanates R 2 Ti 2 O 7 (or R 2 O 3 ·2TiO 2 ), where R = La, Pr, Nd, Sm, Gd, Dy, Er, Yb, Y, which crystallize in either the monoclinic or cubic phases, were synthesized for the first time by the solution-based steric entrapment method. The three-dimensional thermal expansions of these polycrystalline powder samples were measured by in situ synchrotron powder diffraction from 25°C to 1600°C in air, nearly 600°C higher than other in situ thermal expansion studies. The high temperatures in synchrotron experiments were achieved with a quadrupole lamp furnace. Neutron powder diffraction measured the monoclinic phases from 25°C to 1150°C. The La 2 Ti 2 O 7 member of the rare earth di-titanates undergoes a monoclinic to orthorhombic displacive transition on heating, as shown by synchrotron diffraction in air at 885°C (864°C–904°C) and neutron diffraction at 874°C (841°C–894°C).
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Isotropic negative thermal expansion in ZrW2O8 and HfW2O8 from 1100 to 1275◦C
ZrW2O8 (ZrO2•2WO3) and HfW2O8 (HfO2•2WO3) have been the focus of thermal expansion studies due to their isotropic negative thermal expansion (NTE) measured previously at temperatures below 775◦C. This work presents measurements of these materials at their thermodynamically stable temperature ranges of 1105 and 1257◦C for ZrW2O8 and 1105–1276◦C for HfW2O8, where they were characterized with in situ, powder X-ray diffraction. The linear coefficients of thermal expansion were measured to be −5.52 × 10−6 and −4.87 × 10−6◦C−1 for ZrW2O8 and HfW2O8, respectively. The mechanism leading to this NTE is discussed. Powder samples were synthesized by a solution-based process called the organic–inorganic steric entrapment method. In situ characterization in air was carried out at the National Synchrotron Light Source II using a hexapole lamp, optical furnace and theAdvanced Photon Source using a quadrupole lamp, optical furnace to achieve elevated temperatures.
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- Award ID(s):
- 1838595
- PAR ID:
- 10498193
- Editor(s):
- Tatsuki Ohji, Ph. D. Editor
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Edition / Version:
- https://doi.org/10.1111/jace.19721
- Volume:
- 2024
- Issue:
- In press
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- 1-10
- Subject(s) / Keyword(s):
- Equilibrium, HfW2O8, high temperature, in situ, isotropic, negative thermal expansion, synchrotron radiation, ZrW2O8
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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