Growth and property characterization of CaNdGa3O7 and SrNdGa3O7 melilite single crystals
Piezoelectric CaNdGa3O7 and SrNdGa3O7 single crystals with the melilite structure were successfully grown by the Czochralski technique. The thermal properties of these crystals have been systematically investigated. A full matrix of electromechanical material constants was measured by the IEEE resonance method, with k′12 and d14 being on the order of 12.5–14.0% and 9.3–9.4 pC N−1, respectively. A relationship between the physical properties and microstructures was established to explain the anisotropic properties of melilite crystals. In addition, the GaO4 tetrahedral layers, acting as barriers against charge transport, account for the high electrical resistivity along the Z-axis. The high thermal stability of the elastic constants and piezoelectric coefficients of SrNdGa3O7 over the temperature range of 25–600 °C together with its high resistivity on the order of 9.2 × 106 ohm cm at 600 °C make it a promising candidate for piezoelectric sensing applications at high temperatures.