Characterization of high-fracture toughness K-fluorrichterite-fluorapatite glass ceramics

Stoichiometric K-fluorrichterite (Glass A) and the same composition with 2 mol% P2O5 added (Glass B) were prepared and then heat-treated isothermally from 550°1000°C with 50°C intervals. Samples were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The biaxial flexural strength and indentation fracture toughness of heat-treated glass specimens were also determined for both materials. XRD traces and TEM images showed similar phase evolution and fine microstructures for both systems at ≤950°C, with mica and diopside reacting with residual glass to form K-fluorrichterite as the temperature was increased from 650°C. However, in Glass B, fluorapatite was also present at >800°C. In contrast, coarser microstructures were observed at 1000°C, with larger K-fluorrichterite (20 μm) and enstatite (10 μm) crystals in Glasses A and B, respectively. The highest fracture toughness (2.69 ± 0.01 MPa·m(1/2)) and biaxial strength (242.6 ± 3.6 MPa) were recorded for Glass B heat-treated at 1000°C. This was attributed to the presence of enstatite coupled with an interlocked lath-like crystalline microstructure

A Link Between P-Type Electrical Conduction and Microwave Dielectric Loss in Highly Ordered Ba(Co1/3Nb2/3)O-3 Ceramics

BaCo1/3Nb2/3O3 ceramics, with a high density and a similar, high degree of 1:2 B-site cation ordering, exhibit very different quality factors, Q. The ceramics exhibit p-type behavior with higher conductivity and lower Q for samples processed in O2 as compared with those processed in air. It is proposed that unavoidable Co loss during high-temperature ceramic processing leads to p-type doping that must be compensated by oxygen vacancies to impede hole formation. The composition exhibiting only intrinsic conduction and optimized Q is not achieved with processing in atmospheric oxygen due to filling of oxygen vacancies and hole formation during cooling

High throughput synthesis and characterization of the Pb_nNb₂O_5+n (0.5 < n < 4.1) system on a single chip

Most high throughput studies focus on assessing the effect of composition within a single known fundamental structure type, such as perovskite. Here we demonstrate how high throughput synthesis and screening can be used to establish structure–property relations in the PbO–Nb2O5 system, for which eight distinct fundamental structure types are known to exist. PbNb4O11, PbNb2O6 and pyrochlore could be easily distinguished by X-ray diffraction (XRD). However, XRD was insensitive to distortions of the pyrochlore structure and instead Raman spectroscopy was utilized to determine changes in symmetry from cubic to rhombohedral as the PbO concentration increased. High throughput screening of the capacitance revealed permittivity (εr) maxima in the PbNb4O11 (εr = 700) and cubic pyrochlore phases (εr = 450). The εr of PbNb4O11 has not to date been reported but the value for cubic pyrochlore is higher than that reported for bulk ceramics (εr = 270). Initial high electric field studies also revealed exceptionally high tunability (four times that reported for bismuth zinc niobate-based pyrochlores) of the capacitance in the pyrochlore phase.<br/