Discovery of a low thermal conductivity oxide guided by probe structure prediction and machine learning.

We report the aperiodic titanate Ba 10 Y 6 Ti 4 O 27 with a room temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites, and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low thermal conductivity oxides is metastable and located within a quaternary phase field that has been previously explored - its isolation thus requires a precisely-defined synthetic protocol. The necessary narrowing of the search space for experimental investigation is achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that will favour synthetically accessible new compositions and assessment of their properties with machine learning models.