The entropy of a substance increases with its molecular weight and complexity and with temperature. The entropy also increases as the pressure or concentration becomes smaller. Systems at a higher temperature, where molecules move faster on average, have a greater number of possible microstates for how the kinetic energy is distributed, so entropy increases with temperature. High entropy means high disorder and low energy. To better understand entropy, think of a student's bedroom. If no energy or work were put into it, the room would quickly become messy. It would exist in a very disordered state, one of high entropy.

Phase stability is determined (for given temperature and pressure) by the smallest total Delta G of a phase:

Delta G = Delta H - T x Delta S

hence, at high temperature S always 'wins', simply because it grows (stronger) with T.

https://en.wikipedia.org/wiki/Gibbs_free_energy

A good entry into this type of basic thermodynamics thinking is the classical Bragg Williams model, to understand the individual items and trends better, as a basis for thermodynamics-based alloy design (e.g. using Calphad methods):

https://en.wikipedia.org/wiki/Mean-field_theory

A second important aspect here is that the vibrational entropy contributions (as one of the 4 main S contributions in HEAs (mixing, vibr., electronic, magnetic) ) are higher for structures that are more loosely packed as opposed to the closely packed structures such as for instance FCC. Therefore, many of the closed packed metallic structures undergo a phase transformation which is vibrational entropy-stabilized at high temperature to phases which are not so densely packed as the room temperature phases.

Some more specific applications of such generic thermodynamics principles to HEAs are here:

https://www.sciencedirect.com/science/article/abs/pii/S1359645415006278

https://www.nature.com/articles/s41578-019-0121-4

https://www.science.org/doi/full/10.1126/science.abo4940?casa_token=lPX_QizsPlgAAAAA%3Atos-lBewAi1dG-Nvaq6KeeVDzwEfw3F1OoqR8W0ZAQXEpMAPzQG1zfbmxNmzXXRZnnGyAmlmA8MVCu0t

https://www.sciencedirect.com/science/article/abs/pii/S1359645419305002

https://www.nature.com/articles/s41586-022-04935-3

Good luck!

Dr Rana Hamza Shakil thank you for your contribution to the discussion

Systems at a higher temperature, where molecules move faster on average, have a greater number of possible microstates for how the kinetic energy is distributed, so entropy increases with temperature. Entropy changes can also be clearly seen in transitions between phases of matter.Entropy increases as temperature increases. An increase in temperature means that the particles of the substance have greater kinetic energy. The faster-moving particles have more disorder than particles that are moving slowly at a lower temperature. Entropy increases as temperature increases. An increase in temperature means that the particles of the substance have greater kinetic energy. The faster-moving particles have more disorder than particles that are moving slowly at a lower temperature. The entropy of a substance increases with its molecular weight and complexity and with temperature. The entropy also increases as the pressure or concentration becomes smaller. The higher the temperature the more thermal energy the system has; the more thermal energy the system has, the more ways there are to distribute that energy; the more ways there are to distribute that energy, the higher the entropy. Increasing the temperature will increase the entropy. With decrease in temperature, randomness (entropy) decreases because the motion of particles decreases and their velocity decreases so they have less entropy at a lower temperature. The change in entropy (delta S) is equal to the heat transfer (delta Q) divided by the temperature (T). For a given physical process, the entropy of the system and the environment will remain a constant if the process can be reversed. The entropy of a substance increases with its molecular weight and complexity and with temperature. The entropy also increases as the pressure or concentration becomes smaller. Entropies of gases are much larger than those of condensed phases. Entropy generally increases when a reaction produces more molecules than it started with. Entropy generally decreases when a reaction produces fewer molecules than it started with. High entropy means high disorder and low energy. To better understand entropy, think of a student's bedroom. If no energy or work were put into it, the room would quickly become messy. It would exist in a very disordered state, one of high entropy.

Measurement of randomness in a system decides the entropy (S). Randomness is completely based on the atomic arrangement. For example: In solids, atoms are closely packed, so the degree of randomness in less whereas in liquid the atoms are less closely packed and hence the degree of randomness is more.

The temperature (T) seems to have significant influence on the entropy of the system. Following G = H - TS, when the temperature (T) increases, -TS term become dominant. As a result, the atomic arrangement gets disturbed and the vibration sets up within the atoms under the influence of thermal energy (thermal entropy). These vibration creates the atomic spacing at higher temperature and thereby the randomness or entropy increases. Owing to the higher temperature and higher entropy, -TS term became more negative and hence G is also negative. The minimization of the free energy (G) beyond the equilibrium melting temperature assist in the phase transformation and correspondingly stabilizes the liquid phase.

Dr Arnab Sarkar thank you for your contribution to the discussion

The second law states that there exists useful state variable called entropy. The change in entropy (delta S) is equal to the heat transfer (delta Q) divided by the temperature (T). For a given physical process, the entropy of the system and the environment will remain a constant if the process can be reversed.Entropy increases as temperature increases. An increase in temperature means that the particles of the substance have greater kinetic energy. The faster-moving particles have more disorder than particles that are moving slowly at a lower temperature. The entropy of a substance increases with temperature, and it does so for two reasons: As the temperature rises, more microstates become accessible, allowing thermal energy to be more widely dispersed. This is reflected in the gradual increase of entropy with temperature. Systems at a higher temperature, where molecules move faster on average, have a greater number of possible microstates for how the kinetic energy is distributed, so entropy increases with temperature. Entropy changes can also be clearly seen in transitions between phases of matter. Because the change in entropy is Q/T, there is a larger change in Δ S Δ S at lower temperatures (smaller T). The decrease in entropy of the hot (larger T) object is therefore less than the increase in entropy of the cold (smaller T) object, producing an overall increase in entropy for the system. In a chemical reaction, when we increase temperature of any substance, molecular motion increase and so does entropy. Conversely, if the temperature of a substance is lowered, molecular motion decrease, and entropy should decreases. At the microscopic level, the increase in temperature results in greater molecular disorder and an increase in entropy. But the lower volume provides fewer ways to distribute the molecules (energy) reducing disorder and entropy. The result is a net change in entropy of the gas of zero. Entropy always increases with temperature, but it is not directly proportional to temperature. The entropy of water increases enormously when the water transitions from liquid to steam, but the temperature does not change. Entropy always increases with temperature, but it is not directly proportional to temperature. For one obvious example, the entropy of water increases enormously when the water transitions from liquid to steam, but the temperature does not change. The entropy of a substance increases with its molecular weight and complexity and with temperature. The entropy also increases as the pressure or concentration becomes smaller. Entropies of gases are much larger than those of condensed phases. So the entropy change depends on the change of heat energy. The mass, temperature, and specific heat also change the entropy but this change is due to the change in heat caused by these variables. Therefore the root of the entropy change of heat and it can change through various means.