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.