  Phase transition is one of the most important phenomena in nature and plays a
central role in materials design. All phase transitions are characterized by
suitable order parameters, including the order-disorder phase transition.
However, finding a representative order parameter for complex systems is
nontrivial, such as for high-entropy alloys. Given variational autoencoder's
(VAE) strength of reducing high dimensional data into few principal components,
here we coin a new concept of "VAE order parameter". We propose that the
Manhattan distance in the VAE latent space can serve as a generic order
parameter for order-disorder phase transitions. The physical properties of the
order parameter are quantitatively interpreted and demonstrated by multiple
refractory high-entropy alloys. Assisted by it, a generally applicable alloy
design concept is proposed by mimicking the nature mixing of elements. Our
physically interpretable "VAE order parameter" lays the foundation for the
understanding of and alloy design by chemical ordering.
