ENTROPY RELATIONS WITH STRUCTURE AND DYNAMIC PROPERTIES OF OXIDE GLASSES

• Grant number: 25/09121-2
• Support Opportunities: Research Grants - Visiting Researcher Grant - Brazil
• Start date: August 01, 2025
• End date: February 28, 2026
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Edgar Dutra Zanotto
• Grantee: Edgar Dutra Zanotto
• Visiting researcher: Marcio Luis Ferreira Nascimento
• Visiting researcher institution: Escola Politécnica/Epoli/Ufba, Brazil
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 13/07793-6 - CEPIV - Center for Teaching, Research and Innovation in Glass, AP.CEPID

Abstract

Entropy S is an extensive thermodynamic property proposed by Clausius in 1850 and is one of the fundamental concepts of matter. On the other hand, glasses - materials with high entropy compared to their crystalline counterparts - correspond to a state outside the thermodynamic and non-crystalline equilibrium of matter, as defined by Zanotto and Mauro (2017), and still pose numerous fundamental and practical problems.A relatively new concept, whose notion has not yet been properly consolidated, related to S, which includes both configurational and vibrational contributions, called "entropy engineering", has been applied with some success to better understand the glass structure (FENG et al., 2022; 2025), but it is (erroneously) linked to the configurational entropy, Sconf, i.e., which ignores the vibrational aspects. Roughly speaking, this concept, originally proposed by Yeh et al. (2004) for metal alloys, corresponds to the mixing entropy Smix, which is approximated by Sconf, but still without a reasonable definition.According to the renowned American researcher Prabhat Gupta, in personal communication, the difference between the entropies of the supercooled liquid and the crystal at each temperature is defined as the excess entropy, Sexc, which can be approximated by the value of Sconf, which is the difference between the entropies of the supercooled liquid and the glass. The concept in question, proposed by Yeh et al. (2004), is based on the increase in Smix of metal alloys, which, when several chemical elements are mixed, show improvements in several properties such as hardness and corrosion resistance. This concept has recently been suggested to occur in oxide glasses (FENG et al., 2022; 2025). In fact, according to these authors, increasing the entropy Smix (or Sconf) would improve the tendency to form glasses.Therefore, the problem arises to prove the difference between these three variants of entropy and their role in improving the glass-forming ability (GFA), as well as in other dynamic properties related to viscous flow. In this project we propose a new entropy index, which is the sum between absolute zero and the glass transition temperature (Tg) of the entropy difference between the glass and its corresponding crystal at each temperature, the excess entropy, which is close to Sconf for some authors, although there is controversy in this regard.The aim of this research is to contribute to a better understanding of the role of entropy in certain properties of oxide glasses, mainly silicates. We propose to develop and test this new index, which is calculated cumulatively from absolute zero to Tg, resulting in a numerical value ranging from 0 to 1. In this way, we will also be able to define what is a low, medium or high entropy glass (i.e. high entropy index) by calculating this index for different glasses with one to several oxides in their composition.We seek to answer the following questions: Can we use an entropic index to better understand the ease of vitrification and certain dynamic properties of oxide glasses? Is it true that the more chemical elements in a formulation, the easier it is to vitrify? The more elements, the greater the excess entropy? What is the relationship between the three entropies? As far as properties are concerned, the new index proposed here can present relevant developments, for example, what is the relationship of this entropic index with the structure of the glasses, as well as with transport properties, such as the viscosity ¿ and the fragility index m of the same, since, according to the model of Adam and Gibbs (1965), ¿ depends on Sconf and m depends on ¿ in Tg. In short, the methodology will involve calculations, comparisons and analyses using large databases and literature and the possible elaboration of some glasses and the determination of thermodynamic properties, such as specific heat, in addition to Tg and n(T) at the LaMaV / UFSCar. (AU)