Structure and properties of La-modified Na0.5Bi0.5TiO3 at ambient and elevated temperatures

The crystal structure and property changes of sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) piezoelectric ceramics are reported as a function of La modification (0.5–2.0 at. %) and increasing temperature using high resolution x-ray diffraction, permittivity, depolarization, and polarization and strain hysteresis measurements. La substitution is found to decrease the depolarization temperature of NBT (e.g., 1.5 at. % La substitution lowers the depolarization temperature by 60 °C relative to the unmodified composition) with little impact on the room temperature polarization and strain hysteresis. The room temperature structures of the various NBT compositions were modeled using a mixture of the monoclinic Cc space group and the cubic Pmmathm phase, where the Pmmathm phase is used to model local regions in the material which do not obey the long range Cc space group. With increasing La substitution, the lattice parameter distortions associated with the Cc phase approached that of the prototypical cubic unit cell and the fraction of the Pmmathm phase increased. The relationship between these crystallographic changes and the depolarization behavior of La-modified NBT is discussed

Quantification of trace-level silicon doping in AlxGa1–xN films using wavelength-dispersive X-ray microanalysis

Wavelength dispersive X-ray (WDX) spectroscopy was used to measure silicon atom concentrations in the range 35–100 ppm (corresponding to (3–9) ×1018 cm-3) in doped AlxGa1–xN films using an electron probe microanalyser also equipped with a cathodoluminescence (CL) spectrometer. Doping with Si is the usual way to produce the n-type conducting layers that are critical in GaN and AlxGa1–xN-based devices such as LEDs and laser diodes. Previously we have shown excellent agreement for Mg dopant concentrations in p-GaN measured by WDX with values from the more widely used technique of secondary ion mass spectrometry (SIMS). However, a discrepancy between these methods has been reported when quantifying the n-type dopant, silicon. We identify the cause of discrepancy as inherent sample contamination and propose a way to correct this using a calibration relation. This new approach, using a method combining data derived from SIMS measurements on both GaN and AlxGa1–xN samples, provides the means to measure the Si content in these samples with account taken of variations in the ZAF corrections. This method presents a cost effective and time saving way to measure the Si doping and can also benefit from simultaneously measuring other signals, such as CL and electron channeling contrast imaging

Electrical properties of (11-22) Si:AlGaN layers at high Al contents grown by metal-organic vapor phase epitaxy

In this work, the growth and conductivity of semipolar AlxGa1−xN:Si with (11-22) orientation are investigated. AlxGa1−xN:Si (x = 0.60 ± 0.03 and x = 0.80 ± 0.02) layers were grown with different SiH4 partial pressures, and the electrical properties were determined using Hall measurements at room temperature. The aluminum mole fraction was measured by wavelength dispersive x-ray spectroscopy and x-ray diffraction, and the Si-concentration was measured by wavelength dispersive x-ray spectroscopy and secondary ion mass spectroscopy. Layer resistivities as low as 0.024 Ω cm for x = 0.6 and 0.042 Ω cm for x = 0.8 were achieved. For both aluminum mole fractions, the resistivity exhibits a minimum with the increasing Si concentration, which can be explained by compensation due to the formation of cation vacancy complexes at high doping levels. The onset of self-compensation occurs at larger estimated Si concentrations for larger Al contents

In-hospital care, complications, and 4-month mortality following a hip or proximal femur fracture: the Spanish registry of osteoporotic femur fractures prospective cohort study

We have characterised 997 hip fracture patients from a representative 45 Spanish hospitals, and followed them up prospectively for up to 4 months. Despite suboptimal surgical delays (average 59.1 hours), in-hospital mortality was lower than in Northern European cohorts. The secondary fracture prevention gap is unacceptably high at 85%. PURPOSE: To characterise inpatient care, complications, and 4-month mortality following a hip or proximal femur fracture in Spain. METHODS: Design: prospective cohort study. Consecutive sample of patients ≥ 50 years old admitted in a representative 45 hospitals for a hip or proximal femur fragility fracture, from June 2014 to June 2016 and followed up for 4 months post-fracture. Patient characteristics, site of fracture, in-patient care (including secondary fracture prevention) and complications, and 4-month mortality are described. RESULTS: A total of 997 subjects (765 women) of mean (standard deviation) age 83.6 (8.4) years were included. Previous history of fracture/s (36.9%) and falls (43%) were common, and 10-year FRAX-estimated major and hip fracture risks were 15.2% (9.0%) and 8.5% (7.6%) respectively. Inter-trochanteric (44.6%) and displaced intra-capsular (28.0%) were the most common fracture sites, and fixation with short intramedullary nail (38.6%) with spinal anaesthesia (75.5%) the most common procedures. Surgery and rehabilitation were initiated within a mean 59.1 (56.7) and 61.9 (55.1) hours respectively, and average length of stay was 11.5 (9.3) days. Antithrombotic and antibiotic prophylaxis were given to 99.8% and 98.2% respectively, whilst only 12.4% received secondary fracture prevention at discharge. Common complications included delirium (36.1 %) and kidney failure (14.1%), with in-hospital and 4-month mortality of 2.1% and 11% respectively. CONCLUSIONS: Despite suboptimal surgical delay, post-hip fracture mortality is low in Spanish hospitals. The secondary fracture prevention gap is unacceptably high at > 85%, in spite of virtually universal anti-thrombotic and antibiotic prophylaxis