Characterization of Neodymium Calcium Oxyborate Piezoelectric Crystal with Monoclinic Phase

Piezoelectric crystals of neodymium calcium oxyborate, NdCa 4 O(BO 3 ) 3 (NdCOB), were grown by the Czochralski technique. The density was measured using the Archimedes method and found to be 3.63 g/cm 3, 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 α 11 = 8.12, α 13 = 0.680, α 22 = 5.96, and α 33 = 10.3 (10 −6 /°C), respectively. The relative dielectric permittivities were determined to be ε 11 T /ε 0 = 9.90, ε 22 T /ε 0 = 15.5, ε 33 T /ε 0 = 10.2, and ε 13 T /ε 0 = −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 ReCa 4 O(BO 3 ) 3 (Re = rare earth), where NdCOB exhibited relatively higher piezoelectric properties with d 13 = −4.8 pC/N, k 13 = 16.8%, d 26 = 16.5 pC/N, and k 26 = 31.1%, respectively. The relationship between piezoelectric property and structure was explored, in order to further improve the properties of ReCOB crystals.