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The structure of electrically conductive CMAS‐TiO2‐Pd glass and ceramics was investigated by transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), X‐ray photoelectron spectroscopy (XPS), X‐ray absorption near‐edge spectroscopy (XANES), and extended X‐ray absorption fine structure spectroscopy (EXAFS). The XANES spectra of Ti do not show any significant difference between the glasses ceramized in air or in a reducing “forming” gas, as well as between Pd‐containing versus Pd‐free samples, nor between surface versus bulk of the glass‐ceramic samples. However, EXAFS and XANES data recorded at the Pd K‐edge show significant dependences on whether the glass‐ceramic was ceramized in air or in “forming” gas. The XPS spectra of Ti 2p core‐level electrons for glasses ceramized in air or “forming” gas also show a strong difference depending on whether the samples did or did not contain Pd. STEM mapping confirms the existence of grains in the form of main crystalline phases identified with XRD, and also reveals the existence of Pd nanoparticles in glasses ceramized in both air and in “forming” gas.

Barium titanosilicates are possible oxide forms for the immobilization of short-lived fission products in radioactive waste. Ba 2 TiSi 2 O 8 (fresnoite) and BaTiSiO 5 (Ba-titanite) samples were prepared by a solid-state synthesis. The enthalpies of formation of Ba 2 TiSi 2 O 8 crystal and glass at 251C and of BaTi-SiO 5 glass were obtained from drop solution calorimetry in a molten lead borate (2PbO-B 2 O 3 ) solvent at 7011C. The enthalpy of formation for fresnoite composition samples from constituent oxides was exothermic and became more exothermic with increasing crystallinity. Differential scanning calorimetry revealed that the crystallization rate of the fresnoite glasses increased with increasing devitrification. A modified Product Consistency Test-Procedure B (PCT-B) was used to collect solubility data on the fresnoite and titanate phases. The tests suggest that both glassy and crystalline fresnoite exhibit favorable aqueous stability and should be explored further as radioactive waste forms for long-term storage.

An increased need for high‐temperature piezoelectric materials for sensors, some of which must be Pb free due to RoHS regulations, has led to a focused search for suitable materials. Glass–ceramic processing—the controlled crystallization of a precursor glass—offers a unique manner in which to produce partially to wholly crystalline, Pb‐free, and temperature‐stable piezoelectric materials starting with optically homogeneous amorphous materials. Building on previously published work, we have produced NaNbO3‐containing, poled, and pore‐free ferroelectric glass–ceramics that exhibit d33 values of ∼15 pC/N, a dielectric constant of ∼200, an Np frequency constant of ∼3400 Hz·m, and Qm∼60. Nonferroelectric, lithium borosilicate polar glass–ceramics—initially developed by R.E. Newnham and coworkers at Penn State some 20 years ago—have also been produced and yielded d33 values of ∼5 pC/N, although with dielectric constants of <10 they achieved significant g33 values (∼50 × 10−3 V m/N; Np∼4500 Hz·m; Qm∼1500). Room‐temperature planar coupling coefficients of 0.15 and 0.10 were obtained for the polar and ferroelectric varieties, respectively. High‐temperature resonance measurements of both varieties reveal piezoelectricity to at least 600°C for the polar glass–ceramic and up to 300°C for the ferroelectric variety. Excessive conductivity in the polar type, presumably due to high lithium contents, resulted in a strong decrease in resonance amplitude as the temperature was increased. Interestingly, the estimated piezoelectric coefficients for this type showed nearly no temperature dependence and suggest that polar glass–ceramics, lacking a Curie temperature, potentially offer a unique route to high‐temperature piezoelectrics.

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