Non-Centrosymmetric Materials Discovery for Nonlinear Optic and Ferroelectric Applications Using Phonon Database

Materials belonging to non-centrosymmetric point groups, i.e. lacking an inversion center, can exhibit a series of important physical properties such as ferroelectricity (FE) or nonlinear optical (NLO) response. This leads to potential applications in low-power electronic devices, transducers or beyond von-Neumann computers for FE and in lithography and spectroscopy for NLO materials. Discovering new classes of non-centrosymmetric materials is therefore of great interest. Over the last couple of decades, density functional theory (DFT) has become a method of choice for the high-throughput search of new materials thanks to the considerable increase in computational power. Notable early successes of DFT for materials discovery include cathode for electrochemical storage, electrocatalysts or thermoelectrics. Nowadays, properties that used to be computationally-intensive are routinely calculated and in particular, phonons.<br/>Starting from a phonon database, materials with polar imaginary phonon modes are identified as being dynamically unstable. Following the eigenmodes associated with these phonon instabilities, we can assess the energy stability of all the distortions (limited to 2x2x2 supercell) to find out whether the true structural ground-state is polar or not. This method was already applied to the discovery of new ferroelectric materials. Here, I will present some results about the discovery of new classes of non-centrosymmetric material with a focus on a new family with general chemical formula MBa3(B3O6)3 (M=Sc, In, Y, Lu, Eu). Previously reported as belonging to the centrosymmetric space group P6₃/m, our calculations show that the structural ground-state is actually P3 or P6₃. The compound EuBa3(B3O6)3(EBBO) was subsequently synthesized and characterized using XRD and SHG, demonstrating that indeed, it forms into the non-centrosymmetric space group P3. This work shows that new class of NLO and possibly FE materials can be identified through the use of phonon databases.