Thermal properties of the organic nonlinear optical crystal 4-nitro-4′-methylbenzylidene aniline

The thermal properties of high-quality nonlinear optical single crystals of 4-nitro- 4′-methylbenzylidene aniline (NMBA) have been measured in various temperature ranges. The specific heat was measured in the range from 273 to 373 K by differential scanning calorimetry and was found to obey the relationship Cp=2.3×10−3 T+0.487 J g−1 K−1. The peak melting point was detected at a temperature of 402 K with a corresponding enthalpy of melting ΔHm of 113.63 J g−1. Principal thermal expansion and thermal conductivity coefficients were determined at different temperatures. For example, at room temperature (295 K) they were α1=1.274×10−4 K−1, α2=0.826×10−4 K−1, and α3=0.239×10−4 K−1. The principal thermal conductivity coefficients were k1=0.40 W m−1 K−1, k2=0.19 W m−1 K−1, and k3=0.21 W m−1 K−1 and these values were independent of temperature up to 370 K.