Search results for "SAMPLE history"
showing 6 items of 6 documents
Effect of Experimental and Sample Factors on Dehydration Kinetics of Mildronate Dihydrate: Mechanism of Dehydration and Determination of Kinetic Para…
2014
The dehydration kinetics of mildronate dihydrate [3-(1,1,1-trimethylhydrazin-1-ium-2-yl)propionate dihydrate] was analyzed in isothermal and nonisothermal modes. The particle size, sample preparation and storage, sample weight, nitrogen flow rate, relative humidity, and sample history were varied in order to evaluate the effect of these factors and to more accurately interpret the data obtained from such analysis. It was determined that comparable kinetic parameters can be obtained in both isothermal and nonisothermal mode. However, dehydration activation energy values obtained in nonisothermal mode showed variation with conversion degree because of different rate-limiting step energy at hi…
X-ray powder diffraction and LIESST-effect of the spin transition material [Fe(bpp)2](NCS)2·2H2O
2006
Abstract We have studied the X-ray powder diffraction of the spin transition material [Fe(bpp)2](NCS)2 · 2H2O (bpp: 2,6-bis(pyrazol-3-yl)pyridine) at room temperature. Two crystallographic phases have been observed depending on the sample history of this material. The results obtained corroborate the earlier observations from magnetic and calorimetric studies. Relatively prolonged exposure of the sample to X-rays caused a structural change. LIESST and Reverse-LIESST effects, characterised by 57Fe Mossbauer spectroscopy, have been observed in this material.
DIELECTRIC AGEING IN LAYERED FERROELECTRICS
2008
ABSTRACT Studies of the effects of sample history on long-term relaxation of polarization in the Na0.5Bi8.5Ti2Nb4O27 and Na0.5Bi8.5Ti2Ta4O27 ferroelectrics of layered structures are reported. The type of functional relationship of e′(t) at measuring procedures including heating or cooling to the temperature being examined Ta is found to change from exponential (Kohlrausch function) to logarithmic. Results are discussed within the assumption of presence of defect complexes in disordered ferroelectrics.
Relaxor Properties of Barium-Strontium Niobate Ceramics
2011
Dielectric properties of Sr0.75Ba0.25Nb2O6 (SBN-75) ceramics in the range of low and infra-low frequencies are reported. The values of ϵ′ and, in particular of ϵ″, in ceramics are found to be much smaller compared with SBN-75 single crystals below the temperature (Тm) of the ϵ′(T) maximum a sharp increase of the values of dielectric parameters observed above Тm being also different from their thermal behaviour in single crystals. The broadening of phase transition and dependence of the response on sample history are similar to the features observed in other relaxor materials.
Synchrotron powder-diffraction study of the spin transition compound [Fe(bpp)2](NCS)2·2H2O and soft X-ray-induced structural phase conversion
2008
Abstract We have studied the high spin and low spin structural phases of the two-step spin transition compound [Fe(bpp) 2 ](NCS) 2 ·2H 2 O (bpp: 2,6-bis(pyrazol-3-yl)pyridine) of different sample history with X-ray synchrotron ( λ ∼ 0.32 A) powder diffraction at different temperatures as well as with usual X-ray ( λ ∼ 1.54 A) powder diffraction at room temperature by performing rapid repeated scans at regular intervals of time. A structural phase transition occurs only during the first step of the spin transition. Time dependent interconversions of the two crystallographic phases have been observed at room temperature for this material. The results indicate that a soft X-ray (Cu-K α )-ind…
Random-strain-field effects on the low-temperature state of KCN
1991
Random strain fields have been introduced into samples of KCN by pressing pellets from powder and by thermal cycling. X-ray diffractograms show that the low-temperature structure depends strongly on the sample history. In some cycles the noncubic low-temperature phases have been suppressed in mesoscopic surface regions of the samples and the quadrupolar-glass state formed instead.