Characterization of neodymium calcium oxyborate piezoelectric crystal with monoclinic phase

Piezoelectric crystals of neodymium calcium oxyborate, NdCa ₄O(BO₃)₃ (NdCOB), were grown by the Czochralski technique. The density was measured using the Archimedes method and found to be 3.63 g/cm³, in good agreement with the theoretical value. The thermal properties of NdCOB have been investigated, with the specific heat being on the order of 0.550 J/(g C). The four thermal expansion coefficients were measured and found to be ±₁₁ = 8.12, ±₁₃ = 0.680, ±₂₂ = 5.96, and ±₃₃ = 10.3 (10 ^-6/C), respectively. The relative dielectric permittivities were determined to be e11^T/e₀ = 9.90, e22^T/e ₀ = 15.5, e33^T/e₀ = 10.2, and e13 ^T/e₀ = -1.60, respectively, with corresponding low dielectric loss at 100 kHz, being on the order of <0.1%. The complete set of dielectric, elastic, and piezoelectric constants for NdCOB single crystals were determined by the resonance method and compared to other oxyborate crystals ReCa₄O(BO₃)₃ (Re = rare earth), where NdCOB exhibited relatively higher piezoelectric properties with d₁₃ = -4.8 pC/N, k₁₃ = 16.8%, d₂₆ = 16.5 pC/N, and k₂₆ = 31.1%, respectively. The relationship between piezoelectric property and structure was explored, in order to further improve the properties of ReCOB crystals.