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Editorial

Highly Conductive Ceramics with Multiple Types of Mobile Charge Carriers

1
Institute of Nanotechnology and Materials Engineering, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland
2
Advanced Materials Center, Gdańsk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland
3
School of Chemical Engineering, Universidad Industrial de Santander, Bucaramanga 6800002, ST, Colombia
4
School of Materials Science and Engineering, Chonnam National University, Gwangju 61186, Korea
5
Department of Mechanical Engineering, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401, USA
*
Authors to whom correspondence should be addressed.
Submission received: 16 September 2021 / Accepted: 16 September 2021 / Published: 21 September 2021
Functional ceramic materials are of interest in many applications due to their structural and chemical richness and the huge range of physical properties that can be generated and modified by the control of the former (electrical conductivity, thermo-mechanical properties, dielectric, piezoelectric, ferroelectric properties, etc.). Crystalline ionic solids exhibit the unique feature of multiple charge carriers, not only electronic carriers (electrons and holes), but also cationic and anionic carriers, both intrinsically, i.e., as pure phase, and extrinsically, i.e., using the effect of dopants. Their contribution depends on ‘conduction’ mechanisms such as defect formation and interactions, migration paths and barriers, and band structures. This Special Issue focuses on highly conductive ceramics presenting multiple charge carriers. These materials can be classified as mixed electronic and ionic conductors (MIECs) or pure ionic conductors, depending on their respective contributions. The former are studied, for example, as electrode materials for protonic ceramic fuel/electrolysis cells (PCFCs/PCECs) or solid oxide fuel/electrolysis cells (SOFCs/SOECs), while the latter are ideal electrolytes for the same technologies.

1. MIEC

It can be tricky to separate the electronic and ionic contributions when several charge carriers are involved. Pham et al. [1] used the van der Pauw method to determine the conductivity of the cathode composite materials La0.7Sr0.3MnO3±δ (LSM)/Ce0.9Gd0.1O2−δ (GDC) and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)/GDC over a wide temperature range from 800 °C to −73 °C. The samples containing LSM showed reproducible conductivity trajectories, while the LSCF system exhibited unsystematic changes, which may be related to the substantial oxidation/reduction accompanying ferroelastic–paraelastic transitions at 650–750 °C. Combined with structural analysis, they reached the conclusion that a small amount of GDC on the LSCF crystal structures may control the grain size and therefore affect the elastic properties and oxidation/reduction in a subtle way.
Cichy et al. [2] presented the total electrical conductivity of another potential cathode material: the hexagonal rare-earth manganites Y0.95Pr0.05MnO3+δ and Y0.95Nd0.05MnO3+δ. The results were compared to those of the undoped YMnO3+δ. Despite rather small oxygen content variations (≤0.05), the conduction for Y0.95Pr0.05MnO3+δ could be improved by three orders of magnitude over YMnO3+δ. The recorded dependences of the Seebeck coefficient on the temperature in different atmospheres for Y0.95Pr0.05MnO3+δ oxide were found to be complex but generally reflecting the oxygen content variations. The cathodic polarization resistances of Y0.95Pr0.05MnO3+δ highlighted the enhanced reactivity towards oxygen at lower temperatures in air.

2. Ion Conductors

Na-β″-alumina (Na2O~6Al2O3) is known to be an excellent sodium ion conductor, which is used in sodium–sulfur batteries, sodium–nickel chloride batteries, alkali metal thermoelectric converters, and in sensors. Zhu et al. [3] investigated the ion-exchange of Na-β″-alumina + YSZ to form Ag-β″-alumina + YSZ and Li-β″-alumina + YSZ composites. EDS analysis was used to confirm the occurrence of ion exchange. Even though these composites are essentially sodium ion conductors, the oxygen ion conductivity was found to be significant at high temperatures (900 °C). This mixed conduction led to instability of the Ag-β″-alumina + YSZ sample: when heated to 900 °C in air, a thin layer of metallic silver formed on the surface.
The review conducted by Winiarz et al. [4] focuses on protonic ceramic cells, specifically the electrolyte materials (e.g., Ba(Ce,Zr,Y)O3-d) and thin films formed by the pulsed laser deposition (PLD) technique, as well by as using other methods such as RF magnetron sputtering, electron-beam deposition, powder aerosol deposition (PAD), atomic layer deposition (ALD), and spray deposition. Interestingly, the factor that impacts most of the electrical properties of thin films is the film microstructure. The influence of the interface layers, space-charge layers, and strain-modified layers on the total conductivity is also essential but, in many cases, is weaker.

3. Piezoelectric Ceramics

Song et al. [5] characterized the redox behavior, ferroelectric properties, and crystal structure of Ba(1−x)SrxTiO3 ceramics. They concluded that the composition with x = 0.30, referred to as BT-30ST, offers significant advantages in high-precision ceramic actuators with an enhanced electrostrictive coefficient Q33 = larger than 0.034 m4/C2 and an ultra-low hysteresis (<2%) with a high strain (>0.11%).

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Pham, T.; Yu, J.; Lee, J.-S. Conductivity Transitions of La0.7Sr0.3MnOδ and La0.6Sr0.4Co0.2Fe0.8O3−δ in Ce0.9Gd0.1O2−δ Matrix for Dual-Phase Oxygen Transport Membranes. Crystals 2021, 11, 712. [Google Scholar] [CrossRef]
  2. Cichy, K.; Świerczek, K. Influence of Doping on the Transport Properties of Y1−xLnxMnO3+δ (Ln: Pr, Nd). Crystals 2021, 11, 510. [Google Scholar] [CrossRef]
  3. Zhu, L.; Virkar, A. Sodium, Silver and Lithium-Ion Conducting β″-Alumina + YSZ Composites, Ionic Conductivity and Stability. Crystals 2021, 11, 293. [Google Scholar] [CrossRef]
  4. Winiarz, P.; Covarrubias, M.S.C.; Sriubas, M.; Bockute, K.; Miruszewski, T.; Skubida, W.; Jaworski, D.; Laukaitis, G.; Gazda, M. Properties of Barium Cerate-Zirconate Thin Films. Crystals 2021, 11, 1005. [Google Scholar] [CrossRef]
  5. Song, M.; Sun, X.; Li, Q.; Qian, H.; Liu, Y.; Lyu, Y. Enhanced Electrostrictive Coefficient and Suppressive Hysteresis in Lead-Free Ba(1−x)SrxTiO3 Piezoelectric Ceramics with High Strain. Crystals 2021, 11, 555. [Google Scholar] [CrossRef]
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MDPI and ACS Style

Wachowski, S.; Gauthier, G.; Lee, J.-S.; Ricote, S. Highly Conductive Ceramics with Multiple Types of Mobile Charge Carriers. Crystals 2021, 11, 1148. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11091148

AMA Style

Wachowski S, Gauthier G, Lee J-S, Ricote S. Highly Conductive Ceramics with Multiple Types of Mobile Charge Carriers. Crystals. 2021; 11(9):1148. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11091148

Chicago/Turabian Style

Wachowski, Sebastian, Gilles Gauthier, Jong-Sook Lee, and Sandrine Ricote. 2021. "Highly Conductive Ceramics with Multiple Types of Mobile Charge Carriers" Crystals 11, no. 9: 1148. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11091148

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