Studies on vibrational, dielectric, mechanical and thermal properties of organic nonlinear optical co-crystal: 2,6-diaminopyridinium-4-nitrophenolate-4-nitrophenol

This article presents the vibrational, dielectric, mechanical and thermal properties of 2,6-diaminopyridine-4-nitrophenolate-4-nitrophenol co-crystals (DAP:NP) grown by slow evaporation solution growth technique. It crystallizes in orthorhombic noncentrosymmetric space group Pna21 with cell dimension a=10.86 Å, b=12.00 Å and c=13.53 Å; α=β=γ=90° with V=1764 Å3. Functional groups present in the molecule have been identified from FTIR study. Dielectric constant (εr), dielectric loss (tanδ) and ac conductivity (σac) behaviors of the crystals have been studied at different temperatures. Presence of piezoelectric resonance peaks at lower frequency in dielectric measurements may increase the electro-optic coefficient of the crystals. Mechanical strength and its parameters of the grown crystals have been determined by Vickers microhardness test. TG/DTA analysis shows the melting point of the material is 150 °C and it undergoes two stages of decomposition.