Previews of the latest articles in the Journal of the American Ceramic Society

New papers that have been accepted for publication in the Journal of the American Ceramic Society are posted to “Early View” on the Wiley website and can be read even before the issue is printed. Below are summaries of selected papers currently available via Early View.

All members of The American Ceramic Society receive free online access to JACerS. To access any of the ACerS journals, or to become a member, visit www.ceramics.org.

Structural models of mullite phases including sillimanite and ι-Al2O3. Credit: JACerS; Wiley.

Mechanical Properties and Electronic Structure of Mullite Phases Using First-Principles Modeling

Sitaram Aryal, Paul Rulis and Wai-Yim ChingIn

This Feature Article, Aryal, Rulis and Ching from the University of Missouri-Kansas City describe a systematic and detailed theoretical investigation of the structures and properties of the phases in the aluminosilicate series Al_4+2xSi_2-2xO_10-x, where x is 0 to 1. They constructed many stoichiometric supercell models for the four well-known mullite phases in the series (3Al₂O₃∙3SiO₂, 2Al₂O₃∙SiO₂, 4Al₂O₃∙SiO₂ and 9Al₂O₃∙SiO₂) using experimentally reported crystal structures and systematic removal of selected atoms at the partially occupied sites to maintain charge neutrality. Aryal, Rulis and Ching then studied the electronic structure and mechanical properties of the series (as well as sillimanite, where x = 0, and silica-free τ-Al₂O₃, where x = 1) using first-principles calculations. They suggest that the first-principles results explain the experimentally observed structure and properties of mullite phases and their trends with x at the fundamental level.

SEM images of (a) G4 and (b) G6 with the EDS results at the indicated points. Credit: JACerS; Wiley.

Sn-Based Chalcogenide Composite as a High-Capacity Anode Materialfor Lithium Rechargeable Batteries

Youngmin Lee, Suk-Rok Bae, Bong Je Park, Dong Wook Shin, Woon Jin Chung and Yong-Mook Kang

This team of researchers in Korea synthesized high-capacity anode materials from tin-based chalcogenide composites. The team reports that the tin-germanium-sulfur matrix suppresses the volume expansion that can result from alloying between tin and lithium as well as the grain growth associated with the low melting temperature of the tin.

SEM secondary electron micrographs of surface of La2Ni0.9Cu0.1O4+δ sintered at (a) 1350°C and (b) 1450°C for 3 h. Credit: JACerS; Wiley.

Synthesis, Sintering, Transport Properties and Surface Exchange of La₂Ni_0.9Cu_0.1O4+δ

Zuoan Li, Truls Norby and Reidar Haugsrud

These researchers from the University of Oslo used a wet chemical method with optimized ratios of citrate to nitrate and sintering to synthesize dense La₂Ni_0.9Cu_0.1O4+δ ceramics. They report that less citrate decreases the required sintering temperature and improves oxygen permeation. They also report that the oxygen self-diffusion coefficient, oxygen chemical diffusion coefficient and surface exchange coefficient show Arrhenius-type behaviors.

Schematic diagram of experimental set-up. Credit: JACerS; Wiley.

Capacitance Enhancement of Doped Barium Titanate Dielectrics and Multilayer Ceramic Capacitors by aPost-Sintering Thermo-Mechanical Treatment

Olivier Guillon, Jaemyung Chang, Silke Schaab and Suk-Joong L. Kang

This research team from Germany and the Republic of Korea applied a postsintering uniaxial mechanical load to dielectrics and multilayer ceramic capacitors during their cooling to room temperature from either below or above the Curie temperature. The team reports that after load release, the permittivity permanently increased at room temperature by about 8 to 11 percent.

Scanning electron micrograph showing the microstructure of β-eucryptite after etching. An average grain size of about 2 μm is observed. Credit: JACerS; Wiley.

Determining Activation Volume for the Pressure-Induced Phase Transformation in β-Eucryptite through Nanoindentation

Subramanian Ramalingam, Ivar E. Reimanis and Corinne E. Packard

These researchers from the Colorado School of Mines performed hundreds of low-load nanoindentation tests on polycrystalline and single-crystal β-LiAlSiO₄ to characterize its reversible pressure-induced phase transformation to ε-LiAlSiO₄. They report that higher loading rates suppress the deviation from isotropic elastic behavior-a signature of a thermally activated process-and that reversible hysteretic loops occur in the load-displacement curves-consistent with a reversible process during nanoindentation, namely, the phase transformation.

TMA results for selected K- and Na-activated samples with H2O/Al2O3 = 11. Credit: JACerS; Wiley.

Effects of Water Content and Chemical Composition on Structural Properties of Alkaline Activated Metakaolin-Based Geopolymers

Maricela Lizcano, Andres Gonzalez, Sandip Basu, Karen Lozano and Miladin Radovic

A team from Texas A&M University and the University of Texas-Pan American evaluated the effects of chemistry as well as curing and aging conditions on water-loss kinetics, porosity and geopolymer (prepared from a metakaolin and potassium or sodium silicate solutions) structure. The team reports that the amount of water in the initial geopolymer mixture is the most dominant factor that affects density and open porosity of geopolymers after curing and aging and that the SiO₂/Al₂O₃ molar ratio has no direct effect on density and open porosity of the geopolymers.

The structure of ZnO/IDT/NKN-ST-based surface acoustic wave devices. Credit: JACerS; Wiley.

Deposition of Preferred-Orientation ZnO Films on the Lead-Free Ceramic Substrates and Its Effects on the Properties of Surface Acoustic Wave Devices

I-Hao Chan, Jen-Chuan Chang, Chieh-Tze Sun, Mau-Phon Houng and Sheng-Yuan Chu

These researchers from Taiwan used radio-frequency sputtering to grow polycrystalline ZnO films with c-axis orientation on NKN-SrTiO₃ ceramic substrates. They report that the preferred oriented ZnO film is beneficial for improving the electromechanical coupling coefficient of surface acoustic wave devices.

Calculated solvus curve and critical temperature, Τc, of (CaxSr1-x)TiO3 solid solution. Credit: JACerS; Wiley.

Thermochemistry of (Ca_xSr_1-x)TiO₃, (Ba_xSr_1-x)TiO₃, and (Ba_xCa_1-x)TiO₃ Perovskite Solid Solutions

Nissim U. Navi, Roni Z. Shneck, Tatiana Y. Shvareva, Giora Kimmel, Jacob Zabicky, Moshe H. Mintz and Alexandra Navrotsky

This University of California-Davis and Israel research team used high-temperature solution calorimetry in molten 3Na₂O∙MoO₃ solvent to show positive enthalpy of mixing of (Ca_xSr_1-x)TiO₃ and (Ba_xSr_1-x)TiO₃ solid solutions. The team reports the tendency of SrTiO₃ and BaTiO₃ to separate from a CaTiO₃ host matrix, which may be significant in perovskite-bearing nuclear waste ceramics incorporating 90Sr and 137Ba.