Journal of the American Ceramic Society

doi: 10.1111/jace.13053pmid: N/A

MS&T 2013 ACerS Ceramographic Exhibit & Competition Category: Optical, 2nd Place

doi: 10.1111/jace.13052pmid: N/A

Crystallographic anisotropy energy of polarization superimposed on an isothermal ternary section of the ferroelectric solid solution between lead magnesium niobate (PMN), lead zirconate (PZ) and lead titanate (PT). The pseudo‐binary composition‐temperature phase diagrams illustrate how the anisotropy energy varies with the shape of the morphotropic phase boundary along 40% isopleths. See Feature Article by Adam A. Heitmann and George A. Rossetti, Jr. Cover design by Adam A. Heitmann.

Heitmann, Adam A.; Rossetti, George A.

doi: 10.1111/jace.12979pmid: N/A

A thermodynamic analysis is presented for the diffusionless phase diagrams of ferroelectric solid solutions that display a morphotropic phase boundary (MPB) separating adjacent tetragonal and rhombohedral phases. Equations are developed for the shape of the MPB, the locations of triple and tricritical points, and for the line along which the anisotropy of polarization vanishes. The appearance of lower symmetry orthorhombic and monoclinic phases is considered and the topologies of energy surfaces in the region of the phase diagram where these phases may stabilize are illustrated. The theory is applied to the solid solution of lead zirconate with lead titanate (PZT) and relationships between polar anisotropy and the transformation strain, dielectric susceptibility and piezoelectric properties, are discussed. The analysis is used to reproduce phase boundary lines for solid solutions of lead titanate with lead magnesium niobate (PMN‐PT) and lead zinc niobate (PZN‐PT) and composition–temperature diagrams along isopleths in the ternary system PMN‐PZT are estimated. The anisotropies of polarization in solid solutions based on lead titanate and barium titanate are contrasted. The results provide a thermodynamic framework useful for guiding experimental investigations of ferroelectric solid solutions and for generating energy functions used in constitutive modeling and phase field simulations of microstructure and properties.

Zhang, Shaowei; Khangkhamano, Matthana; Zhang, Haijun; Yeprem, Hasibe Aygul; Chamberlain, A.

doi: 10.1111/jace.12945pmid: N/A

Zirconium diboride (ZrB2) powder was synthesized at a low temperature via a molten‐salt‐mediated reduction route using ZrO2, Na2B4O7 and Mg powders as starting raw materials. By using appropriately excessive amounts of Mg and Na2B4O7 to compensate for their evaporation losses, ZrO2 could be completely converted into ZrB2 after 3 h at 1200°C. In addition, the formation of undesirable Mg3B2O6 could be effectively avoided. As‐prepared ZrB2 powders were phase pure, 300–400 nm in size and generally well dispersed. SEM images showed that to a large extent the reactively formed ZrB2 retained the morphology and size of the starting ZrO2. The salt melt formed from MgCl2 and Na2B4O7 at test temperatures is believed to be responsible for the reduced synthesis temperature and good dispersion of the final ZrB2 product powder.

Lonergan, Jason M.; Fahrenholtz, William G.; Hilmas, Greg E.; Trice, R.

doi: 10.1111/jace.12950pmid: N/A

Thermal properties were characterized for zirconium diboride produced by reactive hot pressing and compared to ZrB2 ceramics that were hot pressed from commercial powders. No sintering additives were used in either process. Thermal conductivity was calculated from measured values of heat capacity, thermal diffusivity, and density for temperatures ranging from 298 to 2273 K. ZrB2 produced by reactive hot pressing achieved near full density, but had a small volume fraction of ZrO2, whereas hot‐pressed ZrB2 contained porosity and carbon inclusions. Reactive hot pressing produced a ceramic with higher thermal diffusivity and heat capacity, resulting in thermal conductivities of 127 W·(m·K)−1 at 298 K and 80 W·(m·K)−1 at 2273 K, which were up to ~30% higher than typically reported for hot‐pressed ZrB2.

Wajler, Anna; Kozłowska, Anna; Nakielska, Magdalena; Leśniewska‐Matys, Kamila; Sidorowicz, Agata; Podniesiński, Dariusz; Putyra, Piotr; Harquail Frenc, R.

doi: 10.1111/jace.12965pmid: N/A

Transparent cobalt‐doped magnesium aluminate spinel (Co:MgAl2O4) ceramics with a submicrometer grain size were prepared by spark plasma sintering. For the first time, the nonlinear absorption of Co:MgAl2O4 transparent ceramics was experimentally demonstrated. Both ground state absorption (σGSA) and excited state absorption (σESA) were estimated using the solid‐state slow saturable absorber model based on absorption saturation measurements performed at 1.535 μm. σGSA and σESA for 0.03 at.% Co:MgAl2O4 were found to be 4.1 × 10−19 cm2 and 4.0 × 10−20 cm2, respectively. In the case of 0.06 at.% Co:MgAl2O4 ceramics, σGSA = 2.6 × 10−19 cm2 and σESA= 5.3 × 10−20 cm2 were determined.

Yong, Zehui; He, Lianxing; Li, Bo; Hu, Mingzhe; Lam, Chi Hang; Wang, Yu; Viehland, D.

doi: 10.1111/jace.12958pmid: N/A

Lead magnesium niobate titanate is an important ferroelectric material. In this study, the terahertz (THz) transmission properties of a 0.73Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 single crystal were investigated using a time‐domain spectroscopy method. Complex refractive index and dielectric dispersion functions were determined from the amplitude and phase information derived from time‐domain responses. Based on calculations, it was concluded that the room‐temperature dielectric constant of the single crystal equal to ~30 at 1 THz. This result could be a useful reference for development of ferroelectric‐material‐based THz components and devices.

Ren, Zihe; Zhang, Nan; Long, Xifa; Ye, Zuo‐Guang; Vittayakorn, N.

doi: 10.1111/jace.12966pmid: N/A

A new solid solution of (1−x)Pb(Mg1/2W1/2)O3–xPb(Zn1/2W1/2)O3 has been prepared in the form of ceramics by solid‐state reaction with composition x up to 30%. It is found that with the substitution of Zn2+ for Mg2+ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature TC of PMW increases from 40°C (x = 0) to 67°C (x = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X‐ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group (Pmcn) with a decrease in lattice parameter a, but an increase in b and c as the Zn2+ concentration increases. The low dielectric constant (~ 102), low dielectric loss (tanδ ≈ 10−3), linear‐field‐induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.

Katsumata, Toru; Kubo, Hiromi; Komuro, Shuji; Aizawa, Hiroaki; Ma, L.

doi: 10.1111/jace.12954pmid: N/A

Photoluminescence spectrum, trap depths, and densities of trapped carriers of CaAl2O4:Eu phosphor crystals doped with rare‐earth elements were studied using the thermally stimulated luminescence technique. Trap depths and densities of the specimens vary with rare‐earth elements doped as the auxiliary activators. Tm and Nd are found to be effective for the strong afterglow phosphorescence peaking at λ = 442 nm for several hours after the excitation. CaAl2O4:Eu phosphor crystals doped with Nd and Tm include high density of carriers trapped at E = 0.59 and 0.52 eV, respectively.

Mohanta, Kalyani; Kumar, Ajay; Parkash, Om; Kumar, Devendra; Jayaram, V.

doi: 10.1111/jace.12946pmid: N/A

This study demonstrates a cost‐effective way to fabricate porous ceramics with tailored porosity and pore microstructure using 5–40 wt% rice husk (RH) in <75 μm, 75–180 μm, 180–355 μm, 355–420 μm, and 420–600 μm size, as pore former. Sucrose, used as binder, also acted as a pore former. Porous alumina compacts with 20%–66% volume fraction porosity and 50–516 μm pore size (length) were successfully fabricated. Microstructure of samples reveal randomly oriented elongated coarse pores and fine pores (avg. size 4 μm), created during burnout of RH and sucrose, respectively. Samples with isolated and/or interconnected pores were fabricated using this process. Thermal conductivity of the samples prepared was measured using Transient Plane Source (TPS) technique. Thermal conductivity ranges from 1.2 to 24 W/mK. Experimental results agree closely with predictions made based on Effective Medium Theory (EMT) for a two‐phase system.