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Electronic information and optical properties coupled with the Quantum Theory of Atoms in Molecules (QTAIM) and Electron Localization Function (ELF) analyses are used to elucidate the erbium (Er+3) and praseodymium (Pr+3) intraband f–f transitions in the lithium tantalate (LiTaO3) doped and co-doped configurations and the metal-oxygen bonding. The generalized gradient approximation calculations show that the Er+3- and Pr+3-4f bands appear closer to the conduction band bottom for Er+3 and Pr+3 at the Li sites and to the valance band top for Er+3 at the Ta sites. However, the corresponding hybrid functional calculations for the dopants at the Li site show that the Er+3 and Pr+3-4f bands spread in energy, which agrees with the observed intraband f–f transitions from the optical properties calculations. QTAIM shows that Ta-, Er+3-, and Pr+3-O bonding is incipient covalent for all configurations of this work. The absence of ELF in the metal-O regions aligns with QTAIM on the lack of strong covalent bonding in these compounds. This complementary insight highlights how weakly interacting metal-O atoms lead to delocalized electron density, a feature that influences the physical, electronic, and chemical behavior of the LiTaO3. 

In the last few decades, global energy requirements have grown exponentially, and increased demand is expected in the upcoming decades [...] 

The demand for bone substitutes is increasing in Western countries. Bone graft substitutes aim to provide reconstructive surgeons with off-the-shelf alternatives to the natural bone taken from humans or animal species. Under the tissue engineering paradigm, biomaterial scaffolds can be designed by incorporating bone stem cells to decrease the disadvantages of traditional tissue grafts. However, the effective clinical application of tissue-engineered bone is limited by insufficient neovascularization. As bone is a highly vascularized tissue, new strategies to promote both osteogenesis and vasculogenesis within the scaffolds need to be considered for a successful regeneration. It has been demonstrated that bone and blood vases are piezoelectric, namely, electric signals are locally produced upon mechanical stimulation of these tissues. The specific effects of electric charge generation on different cells are not fully understood, but a substantial amount of evidence has suggested their functional and physiological roles. This review summarizes the special contribution of piezoelectricity as a stimulatory signal for bone and vascular tissue regeneration, including osteogenesis, angiogenesis, vascular repair, and tissue engineering, by considering different stem cell sources entailed with osteogenic and angiogenic potential, aimed at collecting the key findings that may enable the development of successful vascularized bone replacements useful in orthopedic and otologic surgery.