Intrinsic Defects and Their Role in the Phase Transition of Na-Ion Anode Na2Ti3O7.

The development of high-power anode materials for Na-ion batteries is one of the primary obstacles due to the growing demands for their use in the smart grid. Despite the appealingly low cost and non-toxicity, Na2Ti3O7 suffers from low electrical conductivity and poor structural stability, which restricts its use in high-power applications. Viable approaches for overcoming these drawbacks reported to date are aliovalent doping and hydrogenation/hydrothermal treatments, both of which are closely intertwined with native defects. There is still a lack of knowledge, however, of the intrinsic defect chemistry of Na2Ti3O7, which impairs the rational design of high-power titanate anodes. Here, we report hybrid density functional theory calculations of the native defect chemistry of Na2Ti3O7. The defect calculations show that the insulating properties of Na2Ti3O7 arise from the Na and O Schottky disorder that act as major charge compensators. Under high-temperature hydrogenation treatment, these Schottky pairs of Na and O vacancies become dominant defects in Na2Ti3O7, triggering the spontaneous partial phase transition to Na2Ti6O13 and improving the electrical conductivity of the composite anode. Our findings provide an explanation on the interplay between intrinsic defects, structural phase transitions, and electrical conductivity, which can aid understanding of the properties of composite materials obtained from phase transitions.

Preoperative Voice Characteristics in Thyroid Patients.

INTRODUCTION: Thyroid surgery outcomes have evolved from mortality control strategies to morbidity control measures. Most vocal outcomes research in thyroid surgery are focused on recurrent nerve anatomic and functional preservation. However, there are likely multiple causes of vocal dysfunction in thyroid patients. We prospectively analyzed preoperative patients with thyroid disease to define preoperative vocal characteristics of this population. OBJECTIVE: Quantify vocal and laryngeal baseline conditions in thyroid surgical patients. METHODS: Prospective study of preoperative stroboscopy findings and vocal function assessing the correlation between thyroid disease, compressive symptoms, baseline vocal conditions and laryngoscopy results. RESULTS: Vocal quantitative scores were positive for dysphonia in 36% of patients and the Vocal Handicap Index confirmed either slight or Moderate impairment in most patients. Stroboscopy results were abnormal in 60% of cases with no diagnoses of immobility. Correlation was established for diagnosis of cancer and the absence of symptoms. CONCLUSIONS: These results point to a multifactorial cause for vocal impairment in thyroid surgery patients. Research on vocal impairment in thyroid surgery should not be centered exclusively on recurrent nerve neuromonitoring and functional preservation, but also on other variables that may contribute to vocal change in thyroid disease and surgery.

Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na2 Ti3 O7 in Na-Ion Batteries.

Na2 Ti3 O7 (NTO) is considered a promising anode material for Na-ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na+ /Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na2 Ti6 O13 . The enhanced electrochemical performance agrees with the higher Na+ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.