Heating Rate Method Research Articles

Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS2 layered semiconductor

Lanthanum-doped high quality TlInS2 (TlInS2:La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS2:La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS2:La. Thermal treatments of TlInS2:La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T ≤ 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 × 10−14 cm2, corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS2:La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 × 10−16 cm2 were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the direction of the applied electric field and the equilibrium polarization can be reached in a relatively short time. When the polarization field is maintained, while cooling the temperature of sample to a sufficiently low degrees, the relaxation times of the aligned dipoles drastically increases. Practically, frozen internal electric field or electrets states remain inside the TlInS2:La when the applied bias field is switched off. The influence of deep level defects on TSDC spectra of TlInS2:La has been revealed for the first time.

Thermoluminescence of calcium phosphate co-doped with gadolinium and praseodymium

The thermoluminescence of beta-irradiated Ca5(PO4)3OH:Gd3+,Pr3+ is reported. A glow-curve measured at 5 °C s−1 after beta irradiation to 12 Gy revealed an apparently single wide peak at 88 °C. The natural thermoluminescence also showed a single peak with an expanse of over 400 °C. Analysis of the glow-peak after laboratory irradiation using the partial heating procedure Tm–Tstop and its dependence on irradiation was suggestive of the peak being made up of an overlap of closely spaced ones. At least 10 closely collocated components were experimentally recovered using a combination of partial heating and digital mustering. Kinetic analysis of the first three prominent peaks I, II, III using glow-curve deconvolution showed their activation energies to be 0.78 ± 0.01 eV, 0.95 ± 0.01 eV and 1.07 ± 0.01 eV, respectively, and the corresponding frequency factor to be of the order of 1010, 1012 and 1013 s−1 in that order. Complementary analysis using the initial-rise and variable heating rate methods gave similar values for the trap depth. The dose-dependence of the main unresolved peak over the range 6–185 Gy was determined as supralinear using the superlinearity and supralinearity indices.

Thermoluminescence dosimetric characteristics on cubic fluoroperovskite single crystal (KMgF3:Eu2+, Ce3+)

This paper describes investigation of thermoluminescence radiation dosimetry characteristics of Eu2+ doped Potassium Magnesium Fluoride (KMgF3) single crystal co-doped with Ce3+ ions. The perovskite-like KMgF3 polycrystalline compounds were synthesized by standard solid state reaction technique. Phase purity of the synthesized compounds was analyzed by powder X-ray diffraction technique. Single crystals of KMgF3 have been grown from melt by using a vertical Bridgman–Stockbarger method. Thermoluminescence (TL) characteristics of KMgF3 samples doped with Eu2+ and Ce3+ have been studied after β-ray irradiation at room temperature. Order of kinetics (b), activation energy (E), and frequency factor (s) were determined by Chen’s method and variable heating rate method. Results show that the TL glow peak of the KMgF3 samples obeys second-order kinetics. Analysis of the main dosimetric peak by using the methods mentioned above revealed that activation energy (E) is about 1.2eV and the frequency factor (s) is in the range 1010–1011s−1. The TL glow curve structure of the sample remained stable for higher doses of 90Sr/90Y beta source and it shows linearity up to 180Gy. The time dependent fading behavior of the TL characteristics has also been investigated and is found to be quite stable over long time duration. The characteristic Eu2+ emissions are observed in the TL emission spectra.

An investigation of the dosimetric and kinetic properties of sand using ESR and TL techniques

In this research, the general dosimetric and kinetic properties of sand from a beach in southern Turkey were investigated using electron spin resonance (ESR) and thermoluminescence (TL) techniques. The ESR dose response curve presents linear behaviour in the dose range of 250–1000Gy followed by sublinear behaviour in the dose range of 2–8kGy. Kinetic behaviors and activation energy of the free radical were also calculated using the data obtained from annealing studies performed at four different temperatures (220, 240, 260 and 280°C). The activation energy value was calculated as 1.47eV. The long-term fading of the ESR signal at room temperature turned out to be best described by a second-order kinetic decay function. The presence of measurable ESR signal intensity even after a storage period of 90 days was considered as providing an opportunity in the dose estimation of irradiated sand sample. Although the TL glow curve of the natural (unirradiated) sand sample only has a single broad peak at 317°C, the glow curve of the irradiated sample has four glow peaks located at ~115°C, ~156°C, ~231°C and ~308°C and their intensity tends to be increased with absorbed dose.Tmax−Tstopand glow curve fitting results showed that presence of at least five peaks located at ∼116°C, 149°C, 228°C, 306°C and 360°C. This result suggests that the apparently single glow peak D may consist of two or more overlapping glow peaks. According to the thermal fading of the sand sample at room temperature, the TL signal intensities (23°C and 308°C) were found to be quite large after 30 days of storage this allows a more accurate measurement of the glow peak intensity. The additive dose method, variable heating rate method (VHRM), Tmax−Tstop and glow curve fitting method were used to number of peaks, dosimetric properties and kinetic parameters. This study shows that ESR and TL techniques could be successfully used to investigate the kinetics and dosimetric properties of sand sample. Furthermore, the results in this study plus the previous work done by the authors suggest that sand could, by using the ESR and TL techniques, be a suitable material for alternative dose measurement.

Non-isothermal crystallization transformation kinetics analysis and isothermal crystallization kinetics in super-cooled liquid region (SLR) of (Ce0.72Cu0.28)90 − xAl10Fex (x = 0, 5 or 10) bulk metallic glasses

Crystallization transformation kinetics in the non-isothermal and isothermal modes of (Ce0.72Cu0.28)90−xAl10Fex (x=0, 5 or 10) bulk metallic glasses was studied by differential scanning calorimetry (DSC). In the non-isothermal crystallization mode, the various heating rate (VHR) method and Kissinger–Akahira–Sunose (KAS) method were used to analyze the crystallization kinetics. The results revealed that the features of thermal–physical properties and crystallization kinetics are sensitive to iron content. (Ce0.72Cu0.28)90−xAl10Fex (x=0, 5 or 10) bulk metallic glasses show higher stability against crystallization with Fe content increased. The Johnson–Mehl–Avrami (JMA) model was used to analyze the crystallization kinetics in the non-isothermal and isothermal modes. In isothermal mode, the Avrami exponents n for x=0, 5 or 10 are 1.50, 1.86 and 1.56, respectively, which imply that the minor Fe addition might form a new atomic microstructure. The nucleation rate reaches zero when x=0 during the crystallization process; when x=5 or 10, the nucleation size increases by decreasing nucleation rate during crystallization process. In addition, the incubation time is sensitive to annealing temperatures, and the incubation period of crystallization becomes longer as annealing temperature decreases. Finally, the n values of (Ce0.72Cu0.28)90−xAl10Fex (x=0, 5 or 10) bulk metallic glasses were different in the non-isothermal and isothermal modes, indicating different nucleation and growth behaviors in the crystallization process.

Influence of nitrogen implantation on thermoluminescence of synthetic quartz

Thermoluminescence (TL) of synthetic quartz exposed to beta irradiation following implantation with 60 keV N+ ions at fluences ranging between 1 × 1014 and 5 × 1015 ions/cm2 is reported. The glow curve measured at 5°C/s typically consists of a prominent peak near 110°C, studied in this work, and minor glow peaks at around 130°C and 190°C. The TL intensity of the main peak increased both with implantation and with fluence of implantation. The dependence of the intensity on the heating rate and fluence suggests that the implantation introduces new defects that may possibly act as recombination centres. The increase in TL intensity with the heating rate exhibited by implanted samples has been observed in other luminescence materials. This anti-quenching phenomenon has been described as a competition effect between multiple luminescence pathways in luminescence materials. Kinetic analysis of the main glow peak using the initial rise, various heating rate and glow-curve deconvolution methods shows that the activation energy of the main peak is about 0.7 eV with no systematic change due to ion fluence.

Low-Temperature Thermoluminescence Studies on TlInS2Layered Single Crystals

Thermoluminescence characteristics of TlInS2 layered single crystals grown by the Bridgman method were investigated in the low temperature range of 10 300 K. The illuminated sample with blue light (≈ 470 nm) at 10 K was heated at constant heating rate. Curve tting, initial rise and various heating rate methods were used to determine the activation energy of the trap levels. All applied methods showed good consistency about the presence of ve trapping centers located at 14, 19, 350, 420, and 520 meV. Behavior of the TL curve for various heating rates was investigated. Traps distribution has also been studied. The activation energies of the distributed trapping centers were found to be increasing from 14 to 46 meV.

Thermoluminescence glow curve analysis of natural onyx from Turkey

In this study, the thermoluminesce (TL) properties of natural onyx were determined after β-irradiation (90Sr/90Y) at room temperature. The effect of the additive dose and variable heating rate for TL glow peaks of the sample were investigated. Computerized glow curve deconvolution (CGCD) methods were used to determine the number of peaks and kinetic parameters related to the TL glow peaks in natural onyx from Turkey. It was also determined kinetic parameters of onyx by means of the variable heating rate (VHR) method. The sample was exposed to β-irradiation between 2.4Gy and 2.457kGy. The CGCD methods showed that the glow curve of sample is the superposition of at least six first order components which were ascribed as P1-P6. The dose responses of some peaks have similar patterns and they follow linearity. The effect of heating rates on the response of dosimetric glow peaks of sample was studied. The maximum TL peak intensities of glow curve are decreasing with increasing heating rate and maximum TL peak intensities at 1°C/s drops to 20% of the initial value when the sample is read at 6°C/s.

Influence of nitrogen implantation on thermoluminescence of synthetic quartz

Thermoluminescence (TL) of synthetic quartz exposed to beta irradiation following implantation with 60 keV N+ ions at fluences ranging between 1 × 1014 and 5 × 1015 ions/cm2 is reported. The glow curve measured at 5°C/s typically consists of a prominent peak near 110°C, studied in this work, and minor glow peaks at around 130°C and 190°C. The TL intensity of the main peak increased both with implantation and with fluence of implantation. The dependence of the intensity on heating rate and fluence suggests that the implantation introduces new defects that may possibly act as recombination centres. The increase in TL intensity with the heating rate exhibited by implanted samples has been observed in other luminescence materials. This anti-quenching phenomenon has been described as a competition effect between multiple luminescence pathways in luminescence materials. Kinetic analysis of the main glow peak using the initial rise, various heating rate and glow curve deconvolution methods shows that the activation energy of the main peak is about 0.7 eV with no systematic change due to ion fluence.

Effect of heating rate on the thermoluminescence and thermal properties of natural ulexite

Boron-rich compounds are of interest in the nuclear industry because they exhibit a high neutron absorption cross section. The manufacture of these materials involves the application of thermal and chemical treatments. This paper focuses on the study of the effect of the heating rate (HR) in two thermal techniques, differential thermal analysis (DTA) and thermoluminescence (TL), performed on natural ulexite from Bigadiç-Balıkesir (Turkey). The TL measurements were performed at six different heating rates in the range of 25–240°Cmin−1. The UV–blue TL emission of natural ulexite shifted toward higher temperatures with increasing heating rate, whereas the intensity decreased. The kinetic parameters of the ulexite (Ea=0.65(9) eV and s=1.22×1012s−1) were calculated using the variable heating rate method. DTA measurements performed in the range of 0.5–10°Cmin−1 displayed similar behavior to that of the TL response, despite the differences in technique and HR values. The DTA results indicated that natural ulexite exhibits two endothermic peaks originating from different processes: (i) a phase transition between the pentahydrated ulexite phase and a triple-hydrated phase and (ii) dehydration, dehydroxylation and alkali and earth-alkali self-diffusion processes in the ulexite lattice. The main endothermic peak shifted from 160°C to 250°C as the heating rate was increased.

Low temperature thermoluminescence of quaternary thallium sulfide Tl4InGa3S8

Thermoluminescence measurements have been carried out on Tl4InGa3S8 single crystals in the temperature range of 10–300 K at various heating rates. The observed thermoluminescence spectra have been analyzed applying many methods like curve fitting, initial rise, peak shape and heating rate methods. Thermal cleaning method has been performed on the observed thermoluminescence glow curve to separate the overlapped peaks. Three distinctive trapping centers with activation energies of 13, 44 and 208 meV have been revealed from the results of the analysis. Heating rate dependence and traps distribution investigations have been also undertaken on the most intensive peak. The thermoluminescence mechanisms in the observed traps have been attributed to first order kinetics (slow retrapping) on the strength of the consistency between theoretical assumptions for slow retrapping process and experimental outcomes.

Characteristics of traps in Tl2Ga2Se3S single crystals by low‐temperature thermoluminescence measurements

Defect characterization of Tl2Ga2Se3S single crystals has been performed by thermoluminescence (TL) measurements at low temperatures between 10 and 70 K with various heating rate ranging from 0.6 to 1.0 K/s. The TL signal due to the luminescence from trap centers revealed one glow peak having maximum temperature of 36 K. Curve fitting and various heating rate methods were used for the analysis of the glow curve. The activation energy of 13 meV was found by the application of curve fitting method. This practical method also established that the trap center exhibits the characteristics of mixed (general) kinetic order. In addition, various heating rate analysis gave a compatible result (13 meV) with curve fitting as the temperature lag effect was taken into consideration. Distribution of traps was also investigated using an experimental method. A quasi‐continuous distribution was attributed to the determined trap centers.

Synthesis, characterization, photoluminescence and thermally stimulated luminescence investigations of orange red-emitting Sm3+-doped ZnAl2O4 phosphor

Sm3+-doped ZnAl2O4 phosphor was synthesized by citrate sol-gel method and characterized using X-ray diffraction and scanning electron microscopy to identify the crystalline phase and determine the particle size. Photoluminescence (PL) studies on the sample showed emission peaks at 563, 601, 646 and 707 nm with λ ex = 230 nm corresponding to the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions, respectively, due to Sm3+ ions. PL lifetime decay studies confirmed that Sm3+ ions partly entered into the lattice by replacing Al3+ ions and remaining located at the surface of ZnAl2O4 host matrix. Thermally stimulated luminescence (TSL) studies of γ-irradiated Sm3+-doped ZnAl2O4 sample showed two glow peaks at 440 and 495 K, the former being most intense than the latter. The trap parameters were determined using different heating rate methods. Spectral characteristics of the TSL glow showed emission around 565, 599 and 641 nm, indicating the role of Sm3+ ion as the luminescent centre. A probable mechanism for the prominent TSL glow peak, observed at 440 K, was proposed. CIE chromaticity coordinates for the system was evaluated, which suggested that Sm3+-doped ZnAl2O4 could be employed as a potential orange red-emitting phosphor.

Precipitation kinetics of 2519A aluminum alloy based on aging curves and DSC analysis

The precipitation kinetics of 2519A aluminum alloy after different cold rolling reductions before aging was investigated by hardness test and differential scanning calorimetry (DSC). The activation energy was calculated according to DSC curves using single heating rate method. The microstructures of as-rolled and peak-aged alloys were observed by transmission electron microscopy (TEM). The result shows that the age hardenability reduces and the activation energy rises with increasing the reduction from 7% to 40%. Nonuniform dislocations are found in as-rolled alloy and inhomogeneous distribution of θ′ phase is revealed in peak-aged alloy when the reduction is 15%. The inhomogeneous distribution of θ′ phase may be related to the age hardenability reducing and activation energy rising.

On the photo and thermally stimulated luminescence properties of U doped SrBPO5

Un-doped and uranium doped SrBPO5 samples were synthesized using solid-state reaction route and investigated for their photo and luminescence properties. Photoluminescence (PL) spectrum of uranium doped sample showed five peaks at 502, 524, 547, 569 and 597nm. The average frequency of symmetric stretching of O=U=O in the ground electronic state was found to be about 757cm−1. PL decay time measurements on the system confirmed the stabilization of uranium as UO22+ in the matrix. Thermally stimulated luminescence (TSL) measurements carried out on gamma irradiated SrBPO5:U sample showed a glow peak at 390°K, whose spectral characteristics was found to be typical of UO22+. The trap parameters were evaluated using different heating rate method. Room temperature EPR data suggested the formation of borate and oxygen based radical centers in the gamma-irradiated sample. Detailed EPR-TSL correlation studies confirmed the destruction of the oxygen radical to be responsible for the observed glow peak.

Thermoluminescence glow curve for UV induced ZrO2:Ti phosphor with variable concentration of dopant and various heating rate

The present paper reports the synthesis and characterization of Ti doped ZrO2 nanophosphors. The effects of variable concentration of titanium on thermoluminescence (TL) behaviour are studied. The samples were prepared by combustion a synthesis technique which is suitable for less time taking techniques also for large scale production for nano phosphors. The starting material used for sample preparation are Zr(NO3)3 and Ti(NO3)3 and urea used as a fuel. The prepared sample was characterized by X-ray diffraction technique (XRD) with variable concentration of Ti (0.05–0.5 mol%) there is no any phase change found with increase the concentration of Ti. Sample shows cubic structure and the particle size calculated by Scherer's formula. The surface morphology of prepared phosphor was determined by field emission gun scanning electron microscopy (FEGSEM) technique for optimized concentration of dopant. The good connectivity with grains and the semi-sphere like structure was found by FEGSEM. The functional group analysis was determined by Fourier transform infrared (FTIR) spectroscopic techniques. The prepared phosphor examined by thermoluminescence technique. For recording TL glow curve every time 2 mg phosphor was irradiated by UV 254 nm source and fixed the heating rate at 5 °C s−1. Sample shows well resolved peak at 167 °C with a shoulder peak at 376 °C. The higher temperature peak shows the well stability and less fading in prepared phosphor. Also the effect of Ti concentration at fixed UV exposure time was studied. The effect of UV exposure time and dose versus intensity plot was studied. Sample shows linear response with dose and broaden peak with high temperature shows the more stability and less fading in TL glow curve. The linear dose response, high stability and less fading phenomenon shows the sample may be useful for thermoluminescence dosimetry application. Trapping parameters are calculated for every recorded glow curve. The prepared phosphor with optimized concentration of dopant was studied for various heating rate method. The various heating rate (3 °C s−1 to 5 °C s−1) shows shifting in TL glow peaks at higher temperature side. That is opposite behaviour shows in TL glow curve with various heating rate method. The presence of transition metal ions changes (Ti) the TL glow curve structure either enhancing or quenching the TL efficiency. These changes are a consequence of the crystalline field perturbation due to the different characteristics of the dopant ions which supposedly replaces the Zr4+ sites. The traps and the glow curve structure are also dependent upon the morphology of the surface area which in turn depends on the nanocrystallite size. The nanocrystallite size depends also on the dopant ion. Furthermore, the obtained experimental results show that the presence of dopant ions also modifies the TL recombination efficiency which was found to be different for each irradiation type and the specific exposed material. It is important to notice that using the right dopant concentration, it is possible to maximize the TL efficiency and improve sensitivity and dose linearity for a specific irradiation type. For dual TL glow curve present in the sample it is very difficult to calculate the kinetic parameters from peak shape method. The kinetic parameters are calculated by (Computerized glow curve convolution technique) CGCD technique.

Master sintering curves for UO2 and UO2–SiC composite processed by spark plasma sintering

Master sintering curve (MSC) theory has been applied successfully to UO2 and UO2–SiC composite ceramics processed using spark plasma sintering (SPS). By applying the constant heating rate method, where the powder compact was heated at a constant rate to a specified maximum temperature and then cooled naturally, the apparent activation energies for sintering have been determined to be 140kJ/mol for UO2 and 420kJ/mol for UO2–SiC composite. The ability of the derived MSCs to control and predict final density in the sintered compact was demonstrated by additional experimental runs using the isothermal heating method, in which the powder is held for a specified time at the maximum sintering temperature. It is shown that the master sintering curve is an effective tool to characterize the densification and sinterability behavior of a given nuclear powder compact during spark plasma sintering. The reason for significantly lower activation energy in SPS processed UO2 pellets compared to conventional sintering has been rationalized on the basis of field activation in SPS process.

Dosimetric investigations of Tb3+-doped strontium silicate phosphor.

Tb(3+)-doped SrSiO(3) phosphor synthesised by co-precipitation technique exhibits intense green emission due to cross-relaxation phenomena between Tb(3+) ions. Dosimetric properties of this phosphor have been investigated using thermoluminescence (TL) technique. A dosimetrically useful glow peak observed was at 581 K along with a linear dose response over the wide dose range (100 mGy-4 Gy). TL parameters such as trap depth (E), frequency factor (s) and the order of kinetics (b) are determined by different methods such as Chen's peak shape, initial rise, isothermal decay and variable heating rate methods. Results of these methods are compared and reported in this study.

Thermoluminescence characteristics and dosimetric aspects of fluoroperovskites (NaMgF3:Eu2+,Ce3+)

The perovskite-like NaMgF3 polycrystalline powder samples, pure and rare earth doped, were synthesized by conventional solid state reaction method. The perovskite material was doped with 0.2 mol.% of EuF3 and CeF3 impurity. Phase purity of synthesized compounds was analyzed by powder X-ray diffraction technique. The thermoluminescence response of polycrystalline samples showed a linear response up to 12 Gy and then became sub linear at higher doses. The order of kinetics (b), activation energy (E) and other trapping parameters were calculated using peak shape method and variable heating rate method. From glow curve analysis the symmetric factor was calculated. The glow curve showed two peaks at 404 and 488 K, and both of them confirmed the thermoluminescence in the phosphor, which obeyed second-order kinetics. The experimental resulted showed that this phosphor could have potential applications in radiation dosimetry.

Nonisothermal and isothermal oxidative degradation behavior of thermotropic liquid crystal polyesters containing kinked bisphenol AF and bisphenol A units

The polyester P–bisphenol AF 2.5 (BPAF 2.5) and P-bisphenol A 2.5 (BPA 2.5) with low melting temperature and high glass transition temperature can be obtained by introducing 2.5 mol% BPAF/BPA and terephthalic acid (TA) units respectively into the molecular chain of poly(oxybenzoate- co-oxynaphthoate) (P-HBA70). In this study, the nonisothermal and isothermal oxidative degradation behavior of polyester P-BPA2.5 and P-BPAF2.5 were investigated comparatively with parent polyester P-HBA70 by thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy measurements. The introduction of BPAF/BPA units into the molecular chain of P-HBA70 strongly influenced the degradation behavior of polyesters. Four multiple heating rate methods including Kissinger, Kim–Park, Flynn–Wall–Ozawa, and Friedman methods were applied to evaluate the dynamic thermal stability successfully. The following order of the activation energy values: P-BPAF2.5 > P-HBA70 > P-BPA2.5 can be found for the three samples. However, from the results obtained by the standard isoconversional method, the P-BPA2.5 showed a better thermal stability as compared to P-BPAF2.5 under isothermal atmosphere.