Raul Escamilla

Two-dimensional nanomaterials exhibit unique physical phenomena driven by quantum confinement and high surface area. Using ab initio calculations, we evaluate the thickness-dependent properties of 2D ZrB2 across space groups P6/mmm (systems 191-a, 191-b) and P4/nmm (system 129-a) from different thickness levels (from T1 to T4). Material stability is governed by strong covalent sp2 B-B lattices, metallic Zr-Zr sublattices, and hybrid ionic-covalent B (2p-orbital) and Zr (4d and 5s-orbitals) interactions. Metal-terminated surfaces exhibit superior energetic favorability over boron-terminated ones in 191-a. Dynamical instabilities are associated with the softening of acoustic phonon modes involving the Zr-B sublattice. Structurally, system 191-a forms a hexagonal honeycomb configuration with isotropic in-plane elastic behaviour, whereas system 191-b develops thickness-dependent anisotropy associated with its boron-chain arrangement. The system 129-a evolves toward a more uniform bonding environment with increasing thickness. These multifunctional properties establish 2D ZrB2 as a versatile candidate for ultra-incompressible ceramics (191-a), hard nanocoatings (191-b), and protective media (129-a). High Debye temperatures (191-a and 191b) favour nanoscale heat sinks and microchip cooling, while auxetic structures (191-a-T1, 191-b-T1) offer tailored energy absorption for biomedical stents and impact barriers. Additionally, strong broadband optical absorption supports potential application in photodetectors, thermal shields, optical supercapacitors, and infrared plasmonics.

A theoretical study on the phase transition of LaTiO ₃ perovskite under high hydrostatic pressure was conducted using the Density Functional Theory implemented in the CASTEP code and the Hubbard-corrected local density approximation (LDA + U). Results at zero GPa of the lattice parameters, Ti–O bond lengths and bulk modulus are in accordance with experimental data reported by other authors. Enthalpy calculations demonstrate a phase transition (P _T ) from Pbnm to Pm-3 m at 55 GPa, attributable to the hydrostatic pressure induced on the perovskite. Lattice parameters and volume decrease as pressure increases as pressure increases (zero GPa to P _T ), followed by a significant drop post P _T . In addition, the degree of octahedral distortion rises in proportion with the magnitude of pressure applied. Besides, it has been shown that AFM _G behavior is observed during the Pbnm phase, nonetheless, in the Pm-3 m phase, no magnetism is detected. Regarding the elastic properties, a gradual increase in Young’s modulus and Vickers hardness is observed for the Pbnm phase from zero GPa to P _T . While the Pm-3 m phase experiences an exponential increase in Young’s modulus and Vickers hardness (from P _T to 80 GPa). Finally, it has been determined that the bandgap decreases as pressure increases. Nevertheless, post P _T , metallic behavior is obtained. This research reveals LaTiO ₃ perovskite could be a good choice for an electrolyte or anode in energy storage systems.

Currently, incorporating functional materials such as Si and Ge semiconductors on perovskite-type oxide titanates is essential to exploit their electronic and magnetic properties. In this work, the electronic and magnetic properties of Si/Ge monolayer (ML) on a LaO-terminated LaTiO₃ (LTO) or LiO-terminated Li_0.5La_0.5TiO₃ (LLTO) surface, at La-, O- and Li-top sites systems were studied through the Density Functional Theory. Our results show that the system has an antiferromagnetic order when the Si-ML is on the O-top site of the LTO surface; and ferromagnetic when the Si-ML is on the O-top site of the LLTO surface. All the remaining Si adsorption cases are ferrimagnetic systems. When the Ge ML is placed at the La-top and O-top sites on the LTO surface, the resulting systems exhibit ferrimagnetism. In contrast, the Ge-ML on the LLTO surface shows ferromagnetism, regardless of the adsorption site. The adsorption energy values show that the most favorable site to place the Si/Ge ML on the LLTO perovskite surface is at the O-top site. These results display that Si/Ge semiconductor ML/oxide perovskite surface could be used as interface in electrochemical systems.