Dielectric constant and ac and dc electrical conductivity measurements have been performed in single crystals of the fluorite compound , in the temperature range 100 to 770 K. The dielectric response shows both dipolar and charge carrier contributions. The electrical conductivity varied more than 11 orders of magnitude and showed the existence of two thermally activated processes, with activation energies of 1.71(1) eV and 1.17(1) eV, for the higher and lower temperature regions, respectively. The conduction mechanisms have been discussed in terms of the different conduction pathways for the fluorine vacancy motion in the crystal.

The objective of this paper is to present a methodology for the evaluation of uncertainties in the measurements results obtained during the calibration of a digital manovacuometer prototype (DM) with a load cell sensor pressure device incorporated. Calibration curves were obtained for both pressure sensors of the DM using linear regression by weighted least squares method (WLS). Two models were built to evaluate uncertainty. One takes into account the information listed in the sensor datasheet, resulting in the maximum permissible measurement error of the manovacuometer, and the other on the WLS implemented during calibration. Considering a range of ten calibration points, it was found that calibration procedure designed using WLS modeling indicates that the range of measurement uncertainty extends from 0.2 up to 0.5 kPa. This is inside the manufacter range that extends from 1.5 up 3.5 kPa, showing adequacy for use

In this work we present a polarized Raman study of single crystals for several values of the concentration made using different scattering geometries. The Raman spectra, composed of broad bands, have been fitted in accordance with a symmetry analysis which allowed us to assign the vibrational modes, and determine their frequencies and damping constants. The results are compatible with an average hexagonal symmetry for the solid solutions with x in the range . In each of the spectra we found two bands at about 590 and , probably associated with the existence of structures in the solid solutions.

Large Li 3 ThF 7 single crystals have been obtained by the Czochralski technique. Calorimetric and dielectric investigations over a large temperature range ͑100-800 K͒ demonstrate the existence of two additional firstorder phase transitions ͑at about 281 and 467 K͒, beside the known tetragonal-to-orthorhombic one, found at 368 K, 27 K higher than the reported temperature. The knowledge of the structures of these additional phases, besides the phase transition mechanisms, can help to prevent the multiple microcracks which develop in the sample after crystal growth and limit its technological applications. Conductivity measurements show also the high anisotropic character of the Li ϩ ion's mobility.

Raman spectroscopy was used to study pulled Li 3 ThF 7 single crystals between 298 and 403 K, using six special backscattering geometries. The observed Raman bands were very broad, owing to the disorder related to the statistical occupancy of the lithium sites ͑with a 3/4 probability͒. In spite of this, the symmetry rules are well respected assuming an average model with four lithium ions per chemical formula. The spectral evolutions show a structural phase transition occurring at 368 K. After peak deconvolution, we were able to determine and attribute most of the Raman modes corresponding to each phase. The results are compatible with the proposed orthorhombic ͑Ccca͒ to tetragonal ( P4/ncc) structural phase transition, whose ferroelastic nature would be responsible for the appearance of an ordered microcracking pattern in this crystal.

No abstract

Thermographers often use comparative methods to estimate surfaceemissivity. Among the most used is the tape method. In this method a knownemissivity tape in the LWIR (Long Wavelength Infrared) spectrum is placedon the surface to be inspected. After thermal equilibrium, the temperature ofthe tape and the surface under inspection must be the same. In this case, thetemperature observed on the tape is the reference temperature. The emissivityof the surface must then be changed until the reference temperature isreached. It is common practice to admit the value of the emissivity of theadhesive tape as 0.95, there are few studies that present these data withmetrological rigor, which leads to doubts about the emissivity of thecommercial tapes. In this work, experiments were performed on Tekbond,Double A, 3M 101, Rapix, Altape, adhesive tapes for temperatures of 50, 55,60, 65 and 70ºC. An experimental apparatus was developed through which itwas possible to estimate surface reflection, transmission and atmosphericemission for one and two layers of tapes, in order to make emissivitymeasurements possible. Through the data it was possible to statisticallyestimate the LWIR average total hemispheric emissivity as well as theacceptance range to 95% certainty, being therefore equal to ε=0.94±0.03. Itis possible to arm, therefore, that the value of 0.95, usually used as emissivityof the adhesive tape, is extremely reasonable because it is 0.01 of the averagevalue of the Gaussian distribution calculated by this work.

No abstract