Crystal growth, structure and thermal properties of noncentrosymmetric single crystals PrCa4O(BO3)3

Abstract

Noncentrosymmetric praseodymium calcium oxyborate single crystals, PrCa₄O(BO₃)₃ (PrCOB), were grown by the Czochralski technique. The monoclinic unit cell parameters were found to be a = 8.177 Å, b = 16.157 Å, c = 3.629 Å and Z = 2 with space group Cm. Crystal density was measured using the Archimedes method, being on the order of 3.47 g cm⁻³. Thermal properties of PrCOB were investigated, where the specific heat was found to be 0.63 J g⁻¹ °C⁻¹ at room temperature, increasing to 0.85 J g⁻¹ °C⁻¹ at 700 °C. The thermal expansion coefficients were measured to be α₁₁ = 7.99, α₂₂ = 4.90 and α₃₃ = 9.46 (10⁻⁶/°C), respectively. In addition, thermal diffusivity λ₂₂ and thermal conductivity κ₂₂ as a function of temperature were studied, where λ₂₂ was observed to decrease from 0.89 to 0.58 mm² s⁻¹, while κ₂₂ was found to maintain the same value, being ∼1.90 W m⁻¹ °C⁻¹ over the temperature range of 20–700 °C.