@article{ryu_bowes_mcgarrahan_irving_dickey_2021, title={Fermi level pinning in Co-doped BaTiO3: Part I. DC and AC electrical conductivities and degradation behavior}, volume={105}, ISSN={["1551-2916"]}, url={https://doi.org/10.1111/jace.18042}, DOI={10.1111/jace.18042}, abstractNote={AbstractWe explore the synergistic effects of co‐doping BaTiO3 with a judicious combination of acceptors and donors to control the point defect chemistry and electrical properties, with the goal of simultaneously limiting the electronic and ionic conductivities over broad temperature and oxygen partial pressure (pO2) ranges. Specifically, we compare the temperature‐ and pO2‐dependent electrical properties of BaTiO3 ceramics acceptor‐doped with either Mn or Mg and co‐doped with a Y donor. This study, which is the first of a two‐part series, presents the electrical properties as a function of pO2, temperature, and time, focusing on the grain‐interior electrical response. The DC and AC electrical conductivity measurements reveal that co‐doping with Mn and Y can result in (1) increased electrical resistivity over a broad temperature range, (2) pO2‐independent electrical conductivity in oxidizing conditions, and (3) improved time‐dependent dielectric degradation resistance. These behaviors are attributed to a Fermi level pinning effect, as is explained in the companion paper, which presents complementary density functional theory (DFT)‐based grand‐canonical defect chemistry models. The collective experimental and computational studies demonstrate that the pO2‐independent electrical conductivity in the Mn and Y co‐doped BaTiO3 is attributed to a Fermi level pinning mechanism arising from the multivalent Mn dopant, and the background reservoir of positive charge provided by the predominant substitution of Y on the Ba sites. The enhanced degradation resistance is attributed to a reduced oxygen vacancy concentration relative to the other doping chemistries.}, number={1}, journal={JOURNAL OF THE AMERICAN CERAMIC SOCIETY}, publisher={Wiley}, author={Ryu, Gyung Hyun and Bowes, Preston C. and McGarrahan, John R. and Irving, Douglas L. and Dickey, Elizabeth C.}, year={2021}, month={Jul} }
 @article{bowes_ryu_baker_dickey_irving_2021, title={Fermi level pinning in Co-doped BaTiO3: Part II. Defect chemistry models}, volume={7}, ISSN={["1551-2916"]}, url={https://doi.org/10.1111/jace.17938}, DOI={10.1111/jace.17938}, abstractNote={AbstractA first‐principles informed grand canonical defect chemistry model capable of accounting for non‐stoichiometry and partial equilibration of different sub‐lattices is developed and used to study Mg and Mn doped, and (Mg+Y) and (Mn+Y) co‐doped BaTiO3 to elucidate the role of Mn and Y in improving the resistivity and resistance degradation of BaTiO3 as observed by Ryu et al. in Part I of this series of papers. The model qualitatively captures the behavior of the samples in all conditions, reproducing the observed carrier plateau and increased resistivity of (Mn+Y) co‐doped BaTiO3, and expected trends in the concentrations of free oxygen vacancies with doping. These trends reflect the observed differences in degradation characteristics, and help explain the substantially improved degradation resistance of the (Mn+Y) co‐doped samples. Our model adds to the mechanism proposed by Yeoh et al. that the Fermi level is pinned by the multivalent character of MnTi in (Mn+Y) co‐doped BaTiO3 by giving insight into the role of barium vacancies, the site preferences of the dopants, and defect complexes in this mechanism. These insights provide a set of criteria in the search for sets of co‐dopants with similar behaviors.}, number={11}, journal={JOURNAL OF THE AMERICAN CERAMIC SOCIETY}, publisher={Wiley}, author={Bowes, Preston C. and Ryu, Gyung Hyun and Baker, Jonathon N. and Dickey, Elizabeth C. and Irving, Douglas L.}, year={2021}, month={Jul} }
 @article{ryu_hussain_lee_malik_song_kim_kim_2018, title={Lead-free high performance Bi(Zn0.5Ti0.5)O-3-modified BiFeO3-BaTiO3 piezoceramics}, volume={38}, ISSN={["1873-619X"]}, DOI={10.1016/j.jeurceramsoc.2018.05.032}, abstractNote={In this article, structure, dielectric, ferroelectric and piezoelectric properties of Bi rich Bi1.05(Zn0.5Ti0.5)O3-modified BiFeO3-BaTiO3 (BF-BT-xBZT) ceramics were investigated experimentally. Crystal structure, phase purity and microstructure were examined through X-ray diffractometry and scanning electron microscopy, respectively. The crystallographic results show the formation of single-phase solid solutions for all compositions except x = 10 mol%. The BF-BT modification through BZT instigates variation in grain size, enhancement in Curie temperature (TC) and field induced polarization and strain response. Large field induced strain of ∼0.24% at low driving field along with a small hysteresis of ∼38% was observed for 2 mol% BZT modified BF-BT ceramics. These investigated results signpost the potentiality of BF-BT-xBZT ceramics in high temperature piezoelectric device applications.}, number={13}, journal={JOURNAL OF THE EUROPEAN CERAMIC SOCIETY}, author={Ryu, Gyung Hyun and Hussain, Ali and Lee, Myang Hwan and Malik, Rizwan Ahmed and Song, Tae-Kwon and Kim, Won-Jeong and Kim, Myong-Ho}, year={2018}, month={Oct}, pages={4414–4421} }