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Vacancy-Driven Disorder and Elevated Dielectric Response in the Pyrochlore Pb1.5Nb2O6.5

Journal Article · · Inorganic Chemistry
 [1];  [2];  [3];  [4];  [5];  [6];  [2];  [1]
  1. Univ. of Texas, Arlington, TX (United States)
  2. Bates College, Lewiston, ME (United States)
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  4. Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)
  5. Univ. of California, Santa Barbara, CA (United States)
  6. Roanoke College, Salem, VA (United States)
Lone pair-driven distortions are a hallmark of many technologically important lead (Pb)-based materials. Here, the role of Pb2+ in polar perovskites is well understood and easily manipulated for applications in piezo- and ferroelectricity, but the control of ordered lone pair behavior in Pb-based pyrochlores is less clear. Crystallographically and geometrically more complex than the perovskite structure, the pyrochlore structure is prone to geometric frustration of local dipoles due to a triangular arrangement of cations on a diamond lattice. The role of vacancies on the O' site of the pyrochlore network has been implicated as an important driver for the expression and correlation of stereochemically active lone pairs in pyrochlores such as Pb2Ru2O6.5 and Pb2Sn2O6. In this work we report on the structural, dielectric, and heat capacity behavior of the cation- and anion-deficient pyrochlore Pb1.5Nb2O6.5 upon cooling. We find that local distortions are present at all temperatures that can be described by cristobalite-type cation ordering, and this ordering persists to longer length scales upon cooling. From a crystallographic perspective, the material remains disordered and does not undergo an observable phase transition. In combination with density function calculations, we propose that the stereochemical activity of the Pb2+ lone pairs is driven by proximity to O' vacancies, and the crystallographic site disorder of the O' vacancies prohibits long range correlation of lone pair-driven distortions. This in turn prevents a low-temperature phase transition and results in an elevated dielectric permittivity across a broad temperature range.
Research Organization:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Organization:
National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
Grant/Contract Number:
SC0012704
OSTI ID:
2446650
Report Number(s):
BNL--226127-2024-JAAM
Journal Information:
Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 46 Vol. 61; ISSN 0020-1669
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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