skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Transforming an Ionic Conductor into an Electronic Conductor via Crystallization: In Situ Evolution of Transference Numbers and Structure in (La,Sr)(Ga,Fe)O 3‐x Perovskite Thin Films
Title: Transforming an Ionic Conductor into an Electronic Conductor via Crystallization: In Situ Evolution of Transference Numbers and Structure in (La,Sr)(Ga,Fe)O 3‐x Perovskite Thin Films
Abstract Mixed‐conducting perovskites are workhorse electrochemically active materials, but typical high‐temperature processing compromises their catalytic activity and chemo‐mechanical integrity. Low‐temperature pulsed laser deposition of amorphous films plus mild thermal annealing is an emerging route to form homogeneous mixed conductors with exceptional catalytic activity, but little is known about the evolution of the oxide‐ion transport and transference numbers during crystallization. Here the coupled evolution of ionic and electronic transport behavior and structure in room‐temperature‐grown amorphous (La,Sr)(Ga,Fe)O3‐xfilms as they crystallize is explored.In situ ac‐impedance spectroscopy with and without blocking electrodes, simultaneous capturingsynchrotron‐grazing‐incidence X‐ray diffraction, dc polarization, transmission electron microscopy, and molecular dynamics simulations are combined to evaluate isothermal and non‐isothermal crystallization effects and the role of grain boundaries on transference numbers. Ionic conductivity increases by ≈2 orders of magnitude during crystallization, with even larger increases in electronic conductivity. Consequently, as crystallinity increases, LSGF transitions from a predominantly ionic conductor to a predominantly electronic conductor. The roles of evolving lattice structural order, microstructure, and defect chemistry are examined. Grain boundaries appear relatively nonblocking electronically but significantly blocking ionically. The results demonstrate that ionic transference numbers can be tailored over a wide range by tuning crystallinity and microstructure without having to change the cation composition.  more » « less
Award ID(s):
2309037
PAR ID:
10593085
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
Wiley
Date Published:
Journal Name:
Advanced Functional Materials
Volume:
34
Issue:
41
ISSN:
1616-301X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Journal of Materials Chemistry A)
    Recent work has demonstrated a low-temperature route to fabricating mixed ionic/electronic conducting (MIEC) thin films with enhanced oxygen exchange kinetics by crystallizing amorphous-grown thin films under mild temperatures, eluding conditions for deleterious A-site cation surface segregation. Yet, the complex, multiscale chemical and structural changes during MIEC crystallization and their implications for the electrical properties remain relatively unexplored. In this work, micro-structural and atomic-scale structural and chemical changes in crystallizing SrTi 0.65 Fe 0.35 O 3− δ thin films on insulating (0001)-oriented Al 2 O 3 substrates are observed and correlated to changes in the in-plane electrical conductivity, measured in situ by ac impedance spectroscopy. Synchrotron X-ray absorption spectroscopy at the Fe and Ti K-edges gives direct evidence of oxidation occurring with the onset of crystallization and insight into the atomic-scale structural changes driven by the chemical changes. The observed oxidation, increase in B-site polyhedra symmetry, and alignment of neighboring B-site cation coordination units demonstrate increases in both hole concentration and mobility, thus underpinning the measured increase of in-plane conductivity by over two orders of magnitude during crystallization. High resolution transmission electron microscopy and spectroscopy of films at various degrees of crystallinity reveal compositional uniformity with extensive nano-porosity in the crystallized films, consistent with solid phase contraction expected from both oxidation and crystallization. We suggest that this chemo-mechanically driven dynamic nano-structuring is an additional contributor to the observed electrical behavior. By the point that the films become ∼60% crystalline (according to X-ray diffraction), the conductivity reaches the value of dense, fully crystalline films. Given the resulting high electronic conductivity, this low-temperature processing route leading to semi-crystalline hierarchical films exhibits promise for developing high performance MIECs for low-to-intermediate temperature applications. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; (, Advanced Functional Materials)
    Abstract The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) into poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X‐ray data suggest that F4TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π‐stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6–8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F4TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm2V−1s−1in the most crystalline P3HT samples. Temperature‐dependent conductivity measurements show that polaron mobility in SqP‐doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature. 
    more » « less
  3. ; ; ; ; ; ; ; (, Advanced Materials)
    Abstract The structure and packing of organic mixed ionic–electronic conductors have an especially significant effect on transport properties. In operating devices, this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Toward this end, the steady‐state and transient structure of the model organic mixed conductor, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is characterized using multimodal time‐resolved operando techniques. Steady‐state operando X‐ray scattering reveals a doping‐induced lamellar expansion of 1.6 Å followed by 0.4 Å relaxation at high doping levels. Time‐resolved operando X‐ray scattering reveals asymmetric rates of lamellar structural change during doping and dedoping that do not directly depend on potential or charging transients. Time‐resolved spectroscopy establishes a link between structural transients and the complex kinetics of electronic charge carrier subpopulations, in particular the polaron–bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic mixed‐conductor‐based devices, and present the first real‐time observation of the structural changes during doping and dedoping of a conjugated polymer system via X‐ray scattering. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, Polymer Chemistry)
    The commercially available polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is ubiquitous in organic and hybrid electronics. As such, it has often been used as a benchmark material for fundamental studies and the development of new electronic devices. Yet, most studies on PEDOT:PSS have focused on its electronic conductivity in dry environments, with less consideration given to its ion transport, coupled ionic-electronic transport, and charge storage properties in aqueous environments. These properties are essential for applications in bioelectronics (sensors, actuators), charge storage devices, and electrochromic displays. Importantly, past studies on mixed ionic-electronic transport in PEDOT:PSS neglected to consider how the molecular structure of PSS affects mixed ionic-electronic transport. Herein, we therefore investigated the effect of the molecular weight and size distribution of PSS on the electronic properties and morphology of PEDOT:PSS both in dry and aqueous environments, and overall performance in organic electrochemical transistors (OECTs). Using reversible addition–fragmentation chain transfer (RAFT) polymerization with two different chain transfer agents, six PSS samples with monomodal, narrow ( Đ = 1.1) and broad ( Đ = 1.7) size distributions and varying molecular weights were synthesized and used as matrices for PEDOT. We found that using higher molecular weight of PSS ( M n = 145 kg mol −1 ) and broad dispersity led to OECTs with the highest transconductance (up to 16 mS) and [ μC *] values (∼140 F cm −1 V −1 s −1 ) in PEDOT:PSS, despite having a lower volumetric capacitance ( C * = 35 ± 4 F cm −3 ). The differences were best explained by studying the microstructure of the films by atomic force microscopy (AFM). We found that heterogeneities in the PEDOT:PSS films (interconnected and large PEDOT- and PSS-rich domains) obtained from high molecular weight and high dispersity PSS led to higher charge mobility ( μ OECT ∼ 4 cm 2 V −1 s −1 ) and hence transconductance. These studies highlight the importance of considering molecular weight and size distribution in organic mixed ionic-electronic conductor, and could pave the way to designing high performance organic electronics for biological interfaces. 
    more » « less
  5. ; ; ; ; (, ChemRxiv)
    This work presents the synthesis of a molecular crystal of adiponitrile (Adpn) and LiI via a simple melting method. The molecular crystal has both Li+ and I- channels and can be either a Li+ or I- conductor. In the stoichiomnetric crystal (Adpn)2LiI, the Li+ ions interact only with four C≡N groups of Adpn while the I- ions are uncoordinated. Ab initio calculations indicate that the activation energy for ion hopping is less for the I- (Ea = 60 kJ/mol) than for the Li+ (Ea = 93 kJ/mol) ions, and is predominantly an I- conductor, with a lithium-ion transference number (t_Li^+) of t_Li^+ = 0.15, no lithium plating/stripping observed in the cyclic voltammograms (CVs), and a conductivity of σ = 10-4 S/cm at 30 oC. With the addition of excess adiponitrile, which resides in the grain boundaries between the crystal grains, the contribution of Li+ ions to the conductivity increases, so that for the nonstoichiometric molecular crystal (Adpn)3LiI, Li↔ Li^+ redox reactions are observed in the CVs, t_Li^+ = 0.63, conductivity increases to σ = 10-3 S/cm 30 0C, the voltage stability window is 4V, and it is thermally stable to 130 o.C, showcasing the potential of this electrolyte for advanced solid-state Li-I battery applications. The solid (Adpn)3LiI minimizes migration of polyiodides, inhibiting the “shuttle” effect. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email