A₂TiO₅ (A = Dy, Gd, Er, Yb) at High Pressure

Journal Article · Thu Feb 08 00:00:00 EST 2018 · Inorganic Chemistry

DOI:https://doi.org/10.1021/acs.inorgchem.7b03106· OSTI ID:1432057

Park, Sulgiye  ^[1]; Rittman, Dylan R. ^[1]; Tracy, Cameron L. ^[1]; Chapman, Karena W.  ^[2]; Zhang, Fuxiang ^[3]; Park, Changyong  ^[4]; Tkachev, Sergey N. ^[5]; O?Quinn, Eric ^[6]; Shamblin, Jacob  ^[6]; Lang, Maik ^[6]; Mao, Wendy L. ^[7]; Ewing, Rodney C. ^[1]

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1. Stanford Univ., Stanford, CA (United States)
2. Argonne National Lab. (ANL), Argonne, IL (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. Carnegie Institution of Washington, Argonne, IL (United States)
5. Univ. of Chicago, Chicago, IL (United States)
6. Univ. of Tennessee, Knoxville, TN (United States)
7. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)

Here, the structural evolution of lanthanide A₂TiO₅ (A = Dy, Gd, Yb, and Er) at high pressure is investigated using synchrotron X-ray diffraction. The effects of A-site cation size and of the initial structure are systematically examined by varying the composition of the isostructural lanthanide titanates, and the structure of dysprosium titanate polymorphs (orthorhombic, hexagonal and cubic), respectively. All samples undergo irreversible high pressure phase transformations, but with different onset pressures depending on the initial structure. While individual phase exhibits different phase transformation histories, all samples commonly experience a sluggish transformation to a defect cotunnite-like (Pnma) phase for a certain pressure range. Orthorhombic Dy₂TiO₅ and Gd₂TiO₅ form P2₁am at pressures below 9 GPa and Pnma above 13 GPa. Pyrochlore-type Dy₂TiO₅ and Er₂TiO₅ as well as defect-fluorite-type Yb₂TiO₅ form Pnma at ~ 21 GPa, followed by Im3¯m. Hexagonal Dy₂TiO₅ forms Pnma directly, although a small amount of remnants of hexagonal Dy₂TiO₅ is observed even at the highest pressure (~ 55 GPa) reached, indicating a kinetic limitations in the hexagonal Dy₂TiO₅ phase transformations at high pressure. Decompression of these materials leads to different metastable phases. Most interestingly, a high pressure cubic X-type phase (Im3¯m) is confirmed using highresolution transmission electron microscopy on recovered pyrochlore-type Er₂TiO₅. The kinetic constraints on this metastable phase yield a mixture of both the X-type phase and amorphous domains upon pressure release. This is the first observation of an X-type phase for an A₂BO₅ composition at high pressure.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States); Energy Frontier Research Centers (EFRC) (United States). Materials Science of Actinides (MSA)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1432057
• Journal Information: Inorganic Chemistry, Vol. 57, Issue 4; ISSN 0020-1669
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY