Doping Effect on the Electronic Structure and Heat-Storage Properties of Ti₃O₅

Abstract

It is known that substitution of a small fraction of Ti atoms in Ti3O5 by aliovalent metal atoms alters its heat-storage properties, i.e., β → λ phase-transition enthalpy and temperature, and extends its range of application to, for example, the capture and utilization of waste heat. Heat-storage properties vary depending on the substituting element and its concentration. The exploration of the vast space of possible combinations of these quantities is challenging due to the small energy differences under consideration. Thus, computational approaches which reliably predict heat-storage properties of such defective systems can aid in the screening of potential material candidates for subsequent synthesis. Substituted compounds M x Ti3–x O5 with trivalent M = Sc, Al, and Mg have been reported in the literature. Here we present the first thorough study of the doping effect on the electronic structure and the heat-storage properties of Ti3O5 from first principles. Electronic ground states were calculated for all Ti–M substitution positions using the M06 hybrid functional. Doping leads to increased metallic character in both phases, which primarily results from a change in atomic positions and not from the substituting element itself. We applied the r2SCAN-D3 method to the study of heat-storage properties of those materials and found good agreement in phase-transition enthalpies with experimentally recorded data. Calculated phase-transition entropies show larger deviations from experiment. The phase-transition mechanism is studied as a function of the defect concentration by calculating the minimum-energy path. Doping primarily changes the relative energy of both phases and leaves the activation barrier virtually unchanged. Our results suggest that heat-storage systems of this kind are efficient only for M concentrations below 4 atom %.

Anisotropy of the Pressure Effect in the Ti3O5 Phase Transition Process Resolved by Direction-Dependent Interface Propagation

“…We inspected the phonon modes in the 100–200 cm –1 interval, which exhibited acoustic phonon characteristics and identified the involvement of Ti 3 displacements along the c direction as a common feature. Specifically, these modes displace the Ti 3 atoms in an antiparallel fashion resembling the beginning of a rotation, as it is observed in the transition state mode in the β → λ phase transition, which we first identified recently in pristine and doped Ti 3 O 5 as a universal feature of this phase transition. , These modes soften under pressure by Δω ≈ 10 cm –1 , which makes these phonon modes easier to populate and, therefore, opens up a more facile phase transition pathway.…”

Effect of Surface Free Energies and Particle Diameter on the Ti3O5 β → λ Phase Transition Temperature: A Theoretical Study

“…The β → λ phase transition temperature T p , which was earlier calculated with bulk models, 24,28,33 was recalculated by taking surface effects into account (Figure 5(c)).…”

Synthesis of heat storage ceramic λ-Ti3O5 using titanium chloride as the starting material

“…Given the broad availability of metal chlorides for various metals, this approach is a viable candidate for preparing metal-substituted l-Ti 3 O 5 . Although certain metal-substituted l-Ti 3 O 5 has been previously reported, [38][39][40][41][42][43][44][45] those methods typically involve calcination or melting of titanium oxide particles with different metals. The synthesis technique presented in this study offers potential for homogeneous doping using diverse metal chlorides as starting materials to prepare the precursor, enabling greater versatility in the synthesis of metal-substituted l-Ti 3 O 5 .…”