More Like this

1. Relaxor Behavior in Ordered Lead Magnesium Niobate (PbMg 1/3 Nb 2/3 O 3 ) Thin Films

   https://doi.org/10.1002/adfm.201804258  

   Shetty, Smitha ; Damodaran, Anoop ; Wang, Ke ; Yuan, Yakun ; Gopalan, Venkat ; Martin, Lane ; Trolier‐McKinstry, Susan ( November 2018 , Advanced Functional Materials)

   The local compositional heterogeneity associated with the short‐range ordering of Mg and Nb in PbMg_1/3Nb_2/3O₃(PMN) is correlated with its characteristic relaxor ferroelectric behavior. Fully ordered PMN is not prepared as a bulk material. This work examines the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg_2/3Nb_1/3)O₃and PbNbO₃, as suggested by the random‐site model. 100 nm thick, phase‐pure films are grown epitaxially on (111) SrTiO₃substrates using alternate target timed pulsed‐laser deposition of Pb(Mg_2/3Nb_1/3)O₃and PbNbO₃targets with 20% excess Pb. Selected area electron diffraction confirms the emergence of (1/2, 1/2, 1/2) superlattice spots with randomly distributed ordered domains as large as ≈150 nm. These heterostructures exhibit a dielectric constant of 800, loss tangents of ≈0.03 and 2× remanent polarization of ≈11 µC cm⁻²at room temperature. Polarization–electric field hysteresis loops, Rayleigh data, and optical second‐harmonic generation measurements are consistent with the development of ferroelectric domains below 140 K. Temperature‐dependent permittivity measurements demonstrate reduced frequency dispersion compared to short range ordered PMN films. This work suggests a continuum between normal and relaxor ferroelectric behavior in the engineered PMN thin films.

    

   more » « less
2. Exploring the Pb 1− x Sr x HfO 3 System and Potential for High Capacitive Energy Storage Density and Efficiency

   https://doi.org/10.1002/adma.202105967  

   Acharya, Megha ; Banyas, Ella ; Ramesh, Maya ; Jiang, Yizhe ; Fernandez, Abel ; Dasgupta, Arvind ; Ling, Handong ; Hanrahan, Brendan ; Persson, Kristin ; Neaton, Jeffrey B. ; et al ( October 2021 , Advanced Materials)

   The hafnate perovskites PbHfO₃(antiferroelectric) and SrHfO₃(“potential” ferroelectric) are studied as epitaxial thin films on SrTiO₃(001) substrates with the added opportunity of observing a morphotropic phase boundary (MPB) in the Pb_1−xSr_xHfO₃system. The resulting (240)‐oriented PbHfO₃(Pba2) films exhibited antiferroelectric switching with a saturation polarization ≈53 µC cm⁻²at 1.6 MV cm⁻¹, weak‐field dielectric constant ≈186 at 298 K, and an antiferroelectric‐to‐paraelectric phase transition at ≈518 K. (002)‐oriented SrHfO₃films exhibited neither ferroelectric behavior nor evidence of a polarP4mmphase . Instead, the SrHfO₃films exhibited a weak‐field dielectric constant ≈25 at 298 K and no signs of a structural transition to a polar phase as a function of temperature (77–623 K) and electric field (–3 to 3 MV cm⁻¹). While the lack of ferroelectric order in SrHfO₃removes the potential for MPB, structural and property evolution of the Pb_1−xSr_xHfO₃(0 ≤x < 1) system is explored. Strontium alloying increased the electric‐breakdown strength (E_B) and decreased hysteresis loss, thus enhancing the capacitive energy storage density (U_r) and efficiency (η). The composition, Pb_0.5Sr_0.5HfO₃produced the best combination ofE_B = 5.12 ± 0.5 MV cm⁻¹,U_r = 77 ± 5 J cm⁻³, and η = 97 ± 2%, well out‐performing PbHfO₃and other antiferroelectric oxides.

    

   more » « less
3. Connecting the Multiscale Structure with Macroscopic Response of Relaxor Ferroelectrics

   https://doi.org/10.1002/adfm.202006823  

   Otoničar, Mojca ; Bradeško, Andraž ; Fulanović, Lovro ; Kos, Tomaž ; Uršič, Hana ; Benčan, Andreja ; Cabral, Matthew J. ; Henriques, Alexandra ; Jones, Jacob L. ; Riemer, Lukas ; et al ( October 2020 , Advanced Functional Materials)

   Lead‐based relaxor ferroelectrics are characterized by outstanding piezoelectric and dielectric properties, making them useful in a wide range of applications. Despite the numerous models proposed to describe the relation between their nanoscale polar structure and the large properties, the multiple contributions to these properties are not yet revealed. Here, by combining atomistic and mesoscopic‐scale structural analyses with macroscopic piezoelectric and dielectric measurements across the (100–x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃(PMN–xPT) phase diagram, a direct link is established between the multiscale structure and the large nonlinear macroscopic response observed in the monoclinic PMN‐xPT compositions. The approach reveals a previously unrecognized softening effect, which is common to Pb‐based relaxor ferroelectrics and arises from the displacements of low‐angle nanodomain walls, facilitated by the nanoscale polar character and lattice strain disorder. This comprehensive comparative study points to the multiple, distinct mechanisms that are responsible for the large piezoelectric response in relaxor ferroelectrics.

    

   more » « less
4. Scaling effects in the alternating-current poling of thin PIN-PMN-PT single crystals

   https://doi.org/10.1063/5.0084994  

   Kim, Hwang-Pill ; Wan, Haotian ; Lu, Xuanming ; Yamashita, Yohachi ; Jiang, Xiaoning ( April 2022 , Applied Physics Letters)

   AC-poling of Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(PIN-PMN-PT) single crystals with a thickness of 0.06–0.16 mm was studied in this paper. Compared with DC-poled samples, enhancements in piezoelectric and dielectric properties can be obtained when the thickness is above 0.1 mm. However, inconsistency in poling effects was found in the crystals with thickness below 0.1 mm. To elucidate why such scaling effect arises, surface roughness was measured by an atomic force microscopy to correlate surface morphology and poling effects. It was found that non-uniform surface roughness led to inconsistent and decreased properties. Furthermore, temperature-dependent dielectric permittivity spectra were measured to explore how crystal thickness affects the thermal stability of ferroelectric phases. It is noted that complex changes in crystallographic symmetries emanate by decreasing thickness. Such phenomena can be attributed to more influential effects of surface morphology when thickness is reduced. We hope this work suggests a clue for solving the scaling effects of AC-poling on relaxor-PbTiO₃single crystals.

    

   more » « less
5. Special quasirandom structures description of the local structure of disordered Bi 0.5 K 0.5 TiO 3

   https://doi.org/10.1063/5.0123468  

   Jiang, Bo ; Lin, De-Ye ; Wang, Xin ; Selbach, Sverre M. ; Page, Katharine ( December 2022 , Journal of Applied Physics)

   Polar nanoregions (PNRs) are believed to play a decisive role in the local and macroscopic polarization in relaxor ferroelectrics. The limited microscopic understanding of the structure and dynamics of PNRs hampers the rational design of new lead-free materials. Here, the local structure of A-site disordered Bi 0.5 K 0.5 TiO 3 (BKT) is investigated using synchrotron x-ray and neutron pair distribution function (PDF) analysis and density functional theory (DFT) optimized special quasirandom structures (SQSs). DFT-relaxed SQS with a 4 × 4 × 4 supercell size can reproduce the experimental PDFs of disordered BKT, as well as the partial PDFs and total polarization, with comparable results to those reported from a combined analysis of x-ray and neutron PDF data with large-box reverse Monte Carlo methods. We find that small Bi 3+ -rich polar clusters are likely to be the microscopic origin of relaxor behavior in disordered BKT, and that the existence of large polar nanoregions (PNRs) is not necessary to explain the relaxor properties. Our results also highlight the great potential of the SQS approach to gain a nanoscale-to-microscopic understanding of other relaxor solid solutions. 

   more » « less