A series of glass-ceramics were prepared by heat-treatments of 40Na₂O-30MoO₃-30P₂O₅ (in mol%) glass in a temperature range from 380 (T_g) to 490 °C (T_c) and for 1–24 h. The prepared glass-ceramics contain from 2 to 25 wt.% of crystalline NaMoO₂PO₄. The sodium-ion conductivity in these materials decreases up to one order of magnitude with an increase in the degree of crystallization due to the immobilization of sodium ions in crystalline NaMoO₂PO₄. The transport of sodium ions in these materials occurs primarily through the dominant continuous glassy phase, and it is weakly affected by the sporadically distributed crystalline grains. However, the prepared glass-ceramics exhibit high proton conductivity in a humid atmosphere and remarkable humidity-sensing properties; this could be related to crystalline NaMoO₂PO₄, which provides sites for water adsorption. The glass-ceramic prepared at 450 °C for 24 h shows the best humidity-sensing performance among all samples, showing an increase in proton conductivity for more than seven orders of magnitude with the increase in relative humidity from 0% to 95%. Under a highly humid atmosphere (95% relative humidity and 25 °C), the proton conductivity of this glass-ceramic reaches 5.2 × 10⁻³ (Ω cm)⁻¹. Moreover, the electrical response of these materials on the change in the relative humidity is linear and reversible in the entire range of the relative humidity, which indicates that they are novel promising candidates for application as humidity sensors.

We report the effects of thermal oxidation on the sensing properties of porous silicon. Porous silicon substrates were prepared by electrochemical etching and thermally oxidized at different temperatures. A comparative EDS analysis shows that porous surfaces oxidized at higher temperatures have higher oxygen-to-silicon ratios. Our results indicate that the chemoresistive response due to the presence of isopropanol vapors at room temperature also increases with an increasing oxidation temperature. The presence of oxygen atoms in the PS layer could both protect the sensor from further atmospheric oxidation and increase its sensitivity.

High electronically conductive tungsten phosphate glass-ceramics have been prepared by the controlled crystallization of binary 60WO₃–40P₂O₅ glass in the temperature range from 700 to 935 °C and for 1 to 24 h. The substantial increase in the conductivity for four orders of magnitude is a result of the formation of electronically conductive W₂O₃(PO₄)₂ and WO₃ phases. At low crystallization temperature the dominant W₂O₃(PO₄)₂ phase is created, whereas at 935 °C for 24 h the formation of semiconducting WO₃ crystallites of an average size of 80 nm enhances the conductivity to the highest value of 1.64 × 10⁻⁴ (Ω cm)^–1 at 30 °C. The course of the crystallization and its impact on this exceptionally high electronic transport of binary tungsten phosphate glass-ceramics has been discussed in detail. Since such highly electronically conductive WO₃-based glass-ceramics have a great potential as cathode/anode materials in solid state batteries and as electrocatalysts in fuel cells, it is of interest to provide a novel insight into the improvement of their electrical properties.