Why is 4 yuan also called high entropy alloy?

High-entropy alloys usually refer to alloys with almost equal atomic fractions (at least 5%) of more than five main elements. With the development of the research field of high-entropy alloys, it is found that some alloy systems containing four elements can also show similar characteristics to high-entropy alloys, such as high formation entropy and complex solid solutions.

The "high entropy" effect lies not only in the number of elements, but also in whether the entropy contribution of the system is large enough. An alloy of four elements can be considered as a high-entropy alloy if its molar ratio is close to the same amount, and it can form a solid solution and show a high entropy of formation. That is to say, if alloys have similar properties and structures to traditional high-entropy alloys, they can also be classified as high-entropy alloys, even if the number of their main elements is less than five.