The paper by W. L. Bragg and E. J. Williams explores the effect of thermal agitation on the atomic arrangement in alloys, focusing on the formation of superlattices. The authors explain that alloys, unlike chemical compounds, exhibit a dynamic equilibrium where atoms of different types are constantly interchanging positions due to thermal agitation, but the overall structure remains stable. They introduce the concept of a "degree of order" (S) and a potential energy function (V) to describe the system's state, and derive equations to relate these quantities to temperature (T). Key findings include: 1. **Temperature and Order**: The degree of order increases with decreasing temperature, reaching a critical temperature (Tc) below which the system suddenly becomes highly ordered. 2. **Superlattices**: Atoms like AuCu and Fe3Al exhibit superlattice structures where atoms of one type segregate into specific positions, forming a lower-energy arrangement. 3. **Specific Heat and Resistivity**: The specific heat and resistivity of alloys change abruptly at the critical temperature, reflecting the sudden onset of order. 4. **Rate of Approach to Equilibrium**: The time for an alloy to reach equilibrium (τ) depends on temperature and the activation energy required for atomic position interchange. The authors also discuss the implications of these findings for the behavior of alloys during annealing and quenching, and provide experimental evidence to support their theoretical predictions. The study highlights the importance of understanding the dynamic equilibrium in alloys for predicting their physical properties.The paper by W. L. Bragg and E. J. Williams explores the effect of thermal agitation on the atomic arrangement in alloys, focusing on the formation of superlattices. The authors explain that alloys, unlike chemical compounds, exhibit a dynamic equilibrium where atoms of different types are constantly interchanging positions due to thermal agitation, but the overall structure remains stable. They introduce the concept of a "degree of order" (S) and a potential energy function (V) to describe the system's state, and derive equations to relate these quantities to temperature (T). Key findings include: 1. **Temperature and Order**: The degree of order increases with decreasing temperature, reaching a critical temperature (Tc) below which the system suddenly becomes highly ordered. 2. **Superlattices**: Atoms like AuCu and Fe3Al exhibit superlattice structures where atoms of one type segregate into specific positions, forming a lower-energy arrangement. 3. **Specific Heat and Resistivity**: The specific heat and resistivity of alloys change abruptly at the critical temperature, reflecting the sudden onset of order. 4. **Rate of Approach to Equilibrium**: The time for an alloy to reach equilibrium (τ) depends on temperature and the activation energy required for atomic position interchange. The authors also discuss the implications of these findings for the behavior of alloys during annealing and quenching, and provide experimental evidence to support their theoretical predictions. The study highlights the importance of understanding the dynamic equilibrium in alloys for predicting their physical properties.