Reliability of High-Temperature Fixed-Point Installations over 8 Years

At NPL, high-temperature metal-carbon eutectic fixed points have been set up for thermocouple calibration purposes since 2006, for realising reference temperatures above the highest point specified in the International Temperature Scale of 1990 for contact thermometer calibrations. Additionally, cells of the same design have been provided by NPL to other national measurement institutes (NMIs) and calibration laboratories over this period, creating traceable and ISO 17025 accredited facilities around the world for calibrating noble metal thermocouples at \(1324~{^{\circ }}\)C (Co–C) and \(1492~{^{\circ }}\)C (Pd–C). This paper shows collections of thermocouple calibration results obtained during use of the high-temperature fixed-point cells at NPL and, as further examples, the use of cells installed at CCPI Europe (UK) and NIMT (Thailand). The lifetime of the cells can now be shown to be in excess of 7 years, whether used on a weekly or monthly basis, and whether used in an NMI or industrial calibration laboratory.     

Onsite Calibration of a Precision IPRT Based on Gallium and Gallium-Based Small-Size Eutectic Points

Onsite thermometer calibration with temperature scale transfer technology based on fixed points can effectively improve the level of industrial temperature measurement and calibration. The present work performs an onsite calibration of a precision industrial platinum resistance thermometer near room temperature. The calibration is based on a series of small-size eutectic points, including Ga–In (\(15.7 \,{^{\circ }}\hbox {C}\)), Ga–Sn (\(20.5 \,{^{\circ }} \hbox {C}\)), Ga–Zn (\(25.2 \,{^{\circ }} \hbox {C}\)), and a Ga fixed point (\(29.7 \,{^{\circ }} \hbox {C}\)), developed in a portable multi-point automatic realization apparatus. The temperature plateaus of the Ga–In, Ga–Sn, and Ga–Zn eutectic points and the Ga fixed point last for longer than 2 h, and their reproducibility was better than 5 mK. The device is suitable for calibrating non-detachable temperature sensors in advanced environmental laboratories and industrial fields.     

Hysteresis and Instability in Some IPRT Sensors Within Temperature Ranges Extending from $$-196\,^{\circ }\hbox {C}$$ to $$150\,^{\circ }\hbox {C}$$150∘C

Industrial platinum resistance thermometer (IPRT) sensors or probes suffer from some instability on cycling over significant ranges of temperature and, specifically, from hysteresis in which the resistance tends to follow different paths for increasing temperatures compared with decreasing temperatures. The effect is well known, and cases of quite large hysteresis have been reported in the literature. Therefore, in establishing calibration and measurement capabilities for IPRT calibrations it is important to include an assessment of the performance which can be expected of a ‘typical good’ IPRT and to include this in the overall uncertainty which the laboratory can expect to achieve in such calibrations, even though the effect itself is outside the laboratory’s control. This paper presents results which have been obtained in cycling IPRT probes from four sources within various temperature ranges of current interest at NPL, between \(-196\,^{\circ }\hbox {C}\) and \(150\,^{\circ }\hbox {C}\), to see what levels of hysteresis may be expected. The cycles were carried out quite quickly in order to detect the hysteresis before it was mitigated by relaxation effects, but the time dependence was not itself studied. In most cases, hysteresis was \({<}0.0025\,^{\circ }\hbox {C}\) between \(0\,^{\circ }\hbox {C}\) and \(100\,^{\circ }\hbox {C}\), and \({<}0.0035\,^{\circ }\hbox {C}\) when the range extended down to \(-80\,^{\circ }\hbox {C}\) or up to \(150\,^{\circ }\hbox {C}\). Greater instability occurred when the sensors were cooled to \(-196\,^{\circ }\hbox {C}\).     

Small Multiple Fixed-Point Cell as Calibration Reference for a Dry Block Calibrator

A small multiple fixed-point cell (SMFPC) was designed to be used as in situ calibration reference of the internal temperature sensor of a dry block calibrator, which would allow its traceable calibration to the International Temperature Scale of 1990 (ITS-90) in the operating range of the block calibrator from \(70\,^{\circ }\hbox {C}\) to \(430\,^{\circ }\hbox {C}\). The ITS-90 knows in this temperature range, three fixed-point materials (FPM) indium, tin and zinc, with their respective fixed-point temperatures (\(\vartheta _\mathrm {FP}\)), In (\(\vartheta _\mathrm {FP}\,{=}\,156.5985\,^{\circ }\hbox {C}\)), Sn (\(\vartheta _\mathrm {FP}\,{=}\,231.928\,^{\circ }\hbox {C}\)) and Zn (\(\vartheta _\mathrm {FP}\,{=}\,419.527\,^{\circ }\hbox {C}\)). All of these FPM are contained in the SMFPC in a separate chamber, respectively. This paper shows the result of temperature measurements carried out in the cell within a period of 16 months. The test setup used here has thermal properties similar to the dry block calibrator. The aim was to verify the metrological properties and functionality of the SMFPC for the proposed application.     

Thermodynamic Investigation of the Eutectic Mixture of the $$\hbox {LiNO}_{3}$$–$$\hbox {NaNO}_{3}$$NaNO3–$$\hbox {KNO}_{3}$$KNO3–$$\hbox {Ca}(\hbox {NO}_{3})_{2}$$Ca(NO3)2 System

Molten nitrate salt is usually employed as heat transfer or energy storage medium in concentrating solar power systems to improve the overall efficiency of thermoelectric conversion. In the present work, the liquidus curves of the \(\hbox {LiNO}_{3}\)–\(\hbox {NaNO}_{3}\)–\(\hbox {KNO}_{3}\)–\(\hbox {Ca}(\hbox {NO}_{3})_{2}\) system is determined by conformal ionic solution theory according to the solid–liquid equilibrium state of the binary mixture. The calculated eutectic temperature of the mixture is \(93.17\,{^{\circ }}\hbox {C}\), which is close to the experimental value of \(93.22\,{^{\circ }}\hbox {C}\) obtained from differential scanning calorimetry (DSC). Visualization observation experiments reveal that the quaternary eutectic mixture begins to partially melt when the temperature reaches \(50\,{^{\circ }}\hbox {C}\), and the degree of melting increases with temperature. The mixture is completely melted at \(\hbox {130}\,{^{\circ }}\hbox {C}\). The observed changes in the dissolved state at different temperatures correlate well with the DSC heat flow curve fluctuations.     

Design and Investigation of Pd–C Eutectic Fixed-Point Cells for Thermocouple Calibration at NMIA

The calibration of Pt/Rh thermocouples up to 1560 \(^{\circ }\hbox {C}\) at NMIA currently uses the conventional ‘melt-wire technique’ to realize Gold (Au) and Palladium (Pd) melting points, resulting in the loss of 20 mm of wire from the junction end for each calibration. To avoid this loss, NMIA intends to replace the melt-wire technique with the use of miniature fixed-point cells. NMIA has established Copper (Cu) and Cobalt–Carbon (Co–C) eutectic cells for calibration of thermocouples to 1324 \(^{\circ }\hbox {C}\). To extend the calibration up to 1500 \(^{\circ }\hbox {C}\), miniature Palladium–Carbon (Pd–C) eutectic cells (1492 \(^{\circ }\hbox {C}\)) have been constructed and tested in collaboration with NMIJ, AIST. Although these cells are made of high-purity reference materials, careful consideration must be given to contamination introduced during the manufacture and filling of the crucibles and by their long-term use. These issues can only be assessed by measurement of cell-to-cell temperature differences within the ensemble of cells traceable to ITS-90. In the work presented here, 3 NMIA-design mini Pd–C cells were constructed: 1 at NMIA and 2 at NMIJ. These cells were compared, together with a “large” NMIJ Pd–C cell, using type-R, type-B and Pt/Pd thermocouples and radiation thermometry. Although the cells are found to be stable and repeatable, significant problems arising from migration of Pd to the thermocouples were identified.     

Development of the High-Temperature Dew-Point Generator Over the Past 15 Years

At VSL a humidity generator was designed and constructed in the early 1990s. This generator was of the re-circulating-single-pressure type. Over the years, the generator has been thoroughly revised and several critical components have been replaced. Among others the pre-saturator and the change from re-circulation to single-pass mode. Validating experiments showed that the range of the new setup could be extended from \(70\,{^{\circ }}\hbox {C}\) to \(95\,{^{\circ }}\hbox {C}\) dew-point temperature, and the last modification allows an uncertainty of \(0.048\,{^{\circ }}\hbox {C}\) (k = 2) at the maximum temperature. In 2009 the setup was used in the Euramet-T-K8 humidity intercomparison at temperatures up to \(95\,{^{\circ }}\hbox {C}\). In the period from 2003 to 2015, four state-of-the-art chilled mirror hygrometers were regularly calibrated with the generator. One of these was also calibrated with the primary dew-point standards of several other European National Metrology Institutes, which made it possible to link the VSL generator to the generators used in these institutes. An analysis of the results of these calibrations shows an agreement in calibration capabilities within \(0.01\,{^{\circ }}\hbox {C}\) with PTB and NPL.     

High-Accuracy Emissivity Data on the Coatings Nextel 811-21, Herberts 1534, Aeroglaze Z306 and Acktar Fractal Black

The Physikalisch-Technische Bundesanstalt determined the directional spectral emissivities of several widely used black coatings: Nextel 811-21, Herberts 1534, Aeroglaze Z306 and Acktar Fractal Black. These are and were often applied in different industrial and scientific applications. The measurements are taken angularly resolved over a range from \(10{^{\circ }}\) to \(70{^{\circ }}\). They cover the temperature range typical for the application of the respective coating and a wide wavelength range from \(4~\upmu \hbox {m}\) to \(100~\upmu \hbox {m}\). The respective directional total emissivities and hemispherical total emissivities are given as well. The measurements were taken under vacuum at the reduced background calibration facility to achieve low uncertainties and avoid atmospheric interferences. Additionally, some measurements were taken with the emissivity measurement setup in air.     

The Influence of Impurities on the Zinc Fixed Point

Impurities are considered to be the most significant source of uncertainty for the realization of the International Temperature Scale of 1990 by means of metal fixed points. The determination and further reduction in this uncertainty require a traceable chemical analysis of dissolved impurities in the fixed-point metal and accurate knowledge of the specific temperature change caused by impurities (slope of the liquidus line). We determined the slope of the liquidus line for three binary systems and present results and conclusions from the chemical analysis of zinc with a nominal purity of 7N. For the Fe–Zn system, we determined a liquidus slope of (\(-0.91\pm 0.14\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)) from the evaluation of freezing plateaus and (\(-0.76~\pm 0.20\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)) from the evaluation of melting plateaus; for the Pb–Zn system, the corresponding results are (\(-0.27~\pm 0.05\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)) and (\(-0.26~\pm 0.05\)) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)). Although for the Sb–Zn system, we determined a liquidus slope of about \(-0.8\) mK / (\(\upmu \hbox {g}{\cdot }\hbox { g}^{-1}\)), our investigations showed that a correction of the influence of antimony is highly questionable because antimony can be found in zinc in a fully dissolved state or precipitated as an insoluble compound. Iron is the only impurity where a correction of the fixed-point temperature was possible. For the realization of the zinc fixed point at PTB, this correction is between 2 \(\upmu \)K and 16 \(\upmu \)K depending on the batch of zinc used. The influence of the sum of all impurities was estimated by means of the OME method. The resulting uncertainty contribution is between 12 \({\upmu }\hbox {K}\) and 48 \({\upmu }\hbox {K}\).     

Estimating the Kinematic Viscosity of Petroleum Fractions

Kinematic viscosity correlation has been developed for liquid petroleum fractions at 37.78\(\,^{\circ }\hbox {C}\) and \(98.89\,^{\circ }\hbox {C}\) (100 and \(210^{\circ }\hbox {F})\) standard temperatures using a large variety of experimental data. The only required inputs are the specific gravity and the average boiling point temperature. The accuracy of the correlation was compared with several other correlations available in the literature. The proposed correlations proved to be more accurate in predicting the viscosity at 37.78\(\,^{\circ }\hbox {C}\) and \(98.89\,^{\circ }\hbox {C}\) with average absolute deviations of 0.39 and \(0.72\hbox { mm}^{2}/\hbox {s}\), respectively. Another objective was to develop a relation for the variation of viscosity with temperature to predict the viscosity of petroleum fraction at a certain temperature from the knowledge of the viscosity for the same liquid at two other temperatures. The newly developed correlation represents a wide array of temperatures from 20 \(^{\circ }\hbox {C}\) to 150 \(^{\circ }\hbox {C}\) and viscosities from 0.14\(\hbox { mm}^{2}/\hbox {s}\) to 343.64\(\hbox { mm}^{2}/\hbox {s}\). The results have been validated with experimental data consisting of 9558 data points, yielding an overall deviation of \(0.248\hbox { mm}^{2}/\hbox {s}\) and \(\hbox {R}^{2}\) of 0.998. In addition, new formulas were developed to interconvert the viscosity of petroleum fractions from one unit of measure to another based on finding the best fit for a set of experimental data from the literature with \(R^{2}\) as high as 1.0 for many cases. Detailed analysis showed good agreement between the predicted values and the experimental data.     

Structural,dielectric and piezoelectric study of Ca-, Zr-modified $$\hbox {BaTiO}_{3}$$ lead-free ceramics

We prepared a lead-free ceramic (\(\hbox {Ba}_{0.85}\hbox {Ca}_{0.15})(\hbox {Ti}_{1-x}\hbox {Zr}_{x})\hbox {O}_{3}\) (BCTZ) using the conventional mixed oxide technique. The samples were prepared by an ordinary mixing and sintering technique. In this study we investigated how small amounts of \(\hbox {Zr}^{4+}\) can affect the crystal structure and microstructure as well as dielectric and piezoelectric properties of \(\hbox {BaTiO}_{3}\). X-ray diffraction analysis results indicate that no secondary phase is formed in any of the BCTZ powders for \(0 \le x \le 0.1\), suggesting that \(\hbox {Zr}^{4+}\) diffuses into \(\hbox {BaTiO}_{3}\) lattices to form a solid solution. Scanning electron microscopy micrographs revealed that the average grain size gradually increased with \(\hbox {Zr}^{4+}\) content from 9.5 \(\upmu \!\hbox {m}\) for \(x = 0.02\) to 13.5 \(\upmu \!\hbox {m}\) for \(x = 0.1\); Curie temperature decreased due to the small tetragonality caused by \(\hbox {Zr}^{4+}\) addition. Owing to the polymorphic phase transition from orthorhombic to tetragonal phase around room temperature, it was found that the composition \(x = 0.09\) showed improved electrical properties and reached preferred values of \(d_{33} = 148\) pC \(\hbox {N}^{-1}\) and \(K_{\mathrm{p}} = 27\%\).     

Co–C and Pd–C Eutectic Fixed Points for Radiation Thermometry and Thermocouple Thermometry

Two Co–C and Pd–C eutectic fixed point cells for both radiation thermometry and thermocouple thermometry were constructed at NMC. This paper describes details of the cell design, materials used, and fabrication of the cells. The melting curves of the Co–C and Pd–C cells were measured with a reference radiation thermometer realized in both a single-zone furnace and a three-zone furnace in order to investigate furnace effect. The transition temperatures in terms of ITS-90 were determined to be \(1324.18\,{^{\circ }}\hbox {C}\) and \(1491.61\,{^{\circ }}\hbox {C}\) with the corresponding combined standard uncertainty of \(0.44\,{^{\circ }}\hbox {C}\) and \(0.31\,{^{\circ }}\hbox {C}\) for Co–C and Pd–C, respectively, taking into account of the differences of two different types of furnaces used. The determined ITS-90 temperatures are also compared with that of INRIM cells obtained using the same reference radiation thermometer and the same furnaces with the same settings during a previous bilateral comparison exercise (Battuello et al. in Int J Thermophys 35:535–546, 2014). The agreements are within \(k=1\) uncertainty for Co–C cell and \(k = 2\) uncertainty for Pd–C cell. Shapes of the plateaus of NMC cells and INRIM cells are compared too and furnace effects are analyzed as well. The melting curves of the Co–C and Pd–C cells realized in the single-zone furnace are also measured by a Pt/Pd thermocouple, and the preliminary results are presented as well.     

Thermodynamic Temperature Measurement to the Indium Point Based on Radiance Comparison

A multi-national project (the EMRP InK project) was completed recently, which successfully determined the thermodynamic temperatures of several of the high-temperature fixed points above the copper point. The National Metrology Institute of Japan contributed to this project with its newly established absolute spectral radiance calibration capability. In the current study, we have extended the range of thermodynamic temperature measurement to below the copper point and measured the thermodynamic temperatures of the indium point (\(T_{90} =\) 429.748 5 \(\hbox {K}\)), tin point (505.078 K), zinc point (692.677 K), aluminum point (933.473 K) and the silver point (1 234.93 K) by radiance comparison against the copper point, with a set of radiation thermometers having center wavelengths ranging from \(0.65\,\upmu \hbox {m}\) to \(1.6\,\upmu \hbox {m}\). The copper-point temperature was measured by the absolute radiation thermometer which was calibrated by radiance method traceable to the electrical substitution cryogenic radiometer. The radiance of the fixed-point blackbodies was measured by standard radiation thermometers whose spectral responsivity and nonlinearity are precisely evaluated, and then the thermodynamic temperatures were determined from radiance ratios to the copper point. The values of \(T-T_{90}\) for the silver-, aluminum-, zinc-, tin- and indium-point cells were determined as ?4 mK (\(U = 104\,\hbox {mK}, k=2\)), ?99 mK (88 mK), ?76 mK (76 mK), ?68 mK (163 mK) and ?42 mK (279 mK), respectively.     

Dry Block Calibrator with Improved Temperature Field and Integrated Fixed-Point Cells

To reduce uncertainty of calibrations of contact thermometers using dry block calibrators, a concept was developed at Institute for Process Measurement and Sensor Technology of Technische Universität Ilmenau. This concept uses a multi-zone heating, heat flux sensors and a multiple fixed-point cell. The paper shows the concept and its validation on the basis of a dry block calibrator with a working temperature range of \(70\,^{\circ }\hbox {C}\) to \(430\,^{\circ }\hbox {C}\). The experimental results show a stability of \({\pm } 4\,\hbox {mK}\) for the reference temperature and axial temperature differences in the normalization block less than \({\pm }55\,\hbox {mK}\).     

Temperature and Heat Flow Rate Calibration of a Calvet Calorimeter from $$0\,{^{\circ }}\hbox {C}$$ to $$190 \,{^{\circ }}\hbox {C}$$19

This study describes the temperature and heat flow rate calibrations of a Calvet calorimeter (SETARAM, BT2.15) in the temperature range of 0–190 \({^{\circ }}\hbox {C}\). Temperature calibration is carried out using three reference materials, namely water, gallium, and indium, as specified in the International Temperature Scale of 1990 (ITS-90). The sample temperature of the Calvet calorimeter is corrected by the obtained mean value, \(-0.489 \,{^{\circ }}\hbox {C}\), of the measured extrapolated peak onset temperature (\(T_{e})\) when the heating rate (\(\upbeta )\) is zero (\(\Delta T_\mathrm{corr }(\upbeta ~=~0\))). The heat flow rate is calibrated using a reference material with a known heat capacity, namely SRM 720 \(\alpha \)-\(\hbox {Al}_{2}\hbox {O}_{3}\) (synthetic sapphire), which is traceable to the National Institute of Standards and Technology. From the heat flow rate measurements of the blank baseline and SRM 720, the proportional calibration factor, \(\hbox {K}_{\Phi }\), in the 0–190\( \,{^{\circ }}\hbox {C}\) temperature range was determined. The specific heat capacity of copper was measured with the obtained calibration values, and the measured data show consistency with the reference value.     

Resistance-switching properties of Bi-doped $$\hbox {SrTiO}_{3}$$ films for non-volatile memory applications with different device structures

\(\hbox {SrTiO}_{3}\) and Bi-doped \(\hbox {SrTiO}_{3}\) films were fabricated with different device structures using the sol–gel method for non-volatile memory applications, and their resistance-switching behaviour, endurance and retention characteristics were investigated. \(\hbox {SrTiO}_{3}\) and \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si or Pt have the same phase structure, morphologies and grain size; however, the grain size of the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si is slightly larger than those of the \(\hbox {SrTiO}_{3}\) films grown on Si and the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Pt. The \(\hbox {SrTiO}_{3}\) or \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si or Pt all exhibit bipolar resistive-switching behaviour and follow the same conductive mechanism; however, the \(\hbox {Ag}/\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}/\hbox {Si}\) device possesses the highest \(R_{\mathrm{HRS}}{/}R_{\mathrm{LRS}}\) of \(10^{5}\) and the best endurance and retention characteristics. The doping of Bi is conducive to enhance the \(R_{\mathrm{HRS}}{/}R_{\mathrm{LRS}}\) of the \(\hbox {SrTiO}_{3}\) films; meanwhile, the Si substrates help improve the endurance and retention characteristics of the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films.     

Effects of electrolyte concentration and current density on the properties of electro-deposited NiFeW alloy coatings

NiWP alloy coatings were prepared by electrodeposition, and the effects of ferrous chloride (\(\hbox {FeCl}_{2})\), sodium tungstate (\(\hbox {Na}_{2}\hbox {WO}_{4})\) and current density (\(D_{\mathrm{K}}\)) on the properties of the coatings were studied. The results show that upon increasing the concentration of \(\hbox {FeCl}_{2}\), initially the Fe content of the coating increased and then tended to be stable; the deposition rate and microhardness of coating decreased when the cathodic current efficiency (\(\eta \)) initially increased and then decreased; and for a \(\hbox {FeCl}_{2}\) concentration of \(3.6\, \hbox {g\,l}^{-1}\), the cathodic current efficiency reached its maximum of 74.23%. Upon increasing the concentration of \(\hbox {Na}_{2}\hbox {WO}_{4}\), the W content and microhardness of the coatings increased; the deposition rate and the cathode current efficiency initially increased and then decreased. The cathodic current efficiency reached the maximum value of 70.33% with a \(\hbox {Na}_{2}\hbox {WO}_{4}\) concentration of 50 g \(\hbox {l}^{-1}\), whereas the deposition rate is maximum at 8.67 \(\upmu \hbox {m}\,\hbox {h}^{-1}\) with a \(\hbox {Na}_{2}\hbox {WO}_{4}\) concentration of \(40\, \hbox {g\,l}^{-1}\). Upon increasing the \(D_{\mathrm{K}}\), the deposition rate, microhardness, Fe and W content of the coatings increased, the cathodic current efficiency increases first increased and then decreased. When \(D_{\mathrm{K}}\) was 4 A dm\(^{-2}\), the current efficiency reached the maximum of 73.64%.     

Effect of annealing temperature and $$\hbox {CdCl}_{2}$$ treatment on the photo-conversion efficiency of $$\hbox {CdTe/Zn}_{0.1}$$CdTe/Zn0.1$$\hbox {Cd}_{0.9}$$Cd0.9S thin film solar cells

We report the effects of annealing in conjunction with \(\hbox {CdCl}_{2}\) treatment on the photovoltaic properties of \(\hbox {CdTe/Zn}_{0.1}\hbox {Cd}_{0.9}\)S thin film solar cells. CdTe layer is subjected to dry \(\hbox {CdCl}_{2}\) treatment by thermal evaporation method and subsequently, heat treated in air using a tube furnace from 400 to \(500{^{\circ }}\hbox {C}\). AFM and XRD results show improved grain size and crystallographic properties of the CdTe film with dry \(\hbox {CdCl}_{2}\) treatment. This recrystallization and grain growth of the CdTe layer upon \(\hbox {CdCl}_{2}\) treatment translates into improved photo-conversion efficiencies of \(\hbox {CdTe/Zn}_{0.1}\hbox {Cd}_{0.9}\)S cell. The results of dry \(\hbox {CdCl}_{2}\) treatment were compared with conventional wet \(\hbox {CdCl}_{2}\) treatment. Photo-conversion efficiency of 5.2% is achieved for dry \(\hbox {CdCl}_{2}\)-treated cells in comparison with 2.4% of wet-treated cell at heat treatment temperature of \(425{^{\circ }}\hbox {C}\).     

Electrical and Thermal Characteristics of the Insulator–Metal Transition in Crystalline $$\hbox {V}_{2}\hbox {O}_{5}$$ Films

The electrical and thermal properties with respect to the crystallization in \(\hbox {V}_{2}\hbox {O}_{5}\) thin films were investigated by measuring the resistance at different temperatures and applied voltages. The changes in the crystal structure of the films at different temperatures were also explored using Raman measurements. The thermal diffusivity of the crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) film was measured by the nanosecond thermoreflectance method. The microstructures of amorphous and crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) were observed by SEM and XRD measurements. The temperature-dependent Raman spectra revealed that a structural phase transition does not occur in the crystalline film. The resistance measurements of an amorphous film indicated semiconducting behavior, whereas the resistance of the crystalline film revealed a substantial change near \(250\,{^{\circ }}\hbox {C}\), and Ohmic behavior was observed above \(380\,{^{\circ }}\hbox {C}\). This result was due to the metal–insulator transition induced by lattice distortion in the crystalline film, for which \(T_{\mathrm{c}}\) was \(260\,{^{\circ }}\hbox {C}\). \(T_{\mathrm{c}}\) of the film decreased from 260 \({^{\circ }}\hbox {C}\) to \(230\,{^{\circ }}\hbox {C}\) with increasing applied voltage from 0 V to 10 V. Furthermore, the thermal diffusivity of the crystalline film was \(1.67\times 10^{-7}\,\hbox {m}^{2}\cdot \hbox {s}^{-1}\) according to the nanosecond thermoreflectance measurements.     

Influence of $$\hbox {TiO}_{2}$$ particle size and conductivity of the CuCrO$$_{2}$$2 nanoparticles on the performance of solid-state dye-sensitized solar cells

Solid-state dye-sensitized solar cells have been fabricated with mesoporous \(\hbox {TiO}_{2 }\) photoanode and N719 dye as photosensitizer. First, \(\hbox {TiO}_{2}\) and non-doped, Zn- and Mg-doped CuCrO\(_{2}\) nanoparticles have been synthesized by sol–gel method. In addition, the \(\hbox {TiO}_{2}\) pastes have been prepared through Pechini-type sol–gel method. The effect of \(\hbox {TiO}_{2}\) particle size, mesoporous \(\hbox {TiO}_{2}\) photoanode thickness and solid-state electrolyte thickness on the efficiency of the fabricated devices has been investigated. Our results show that in spite of the low amount of dye loading for photoanode with large \(\hbox {TiO}_{2}\) nanoparticles (80–180 nm), the dye-sensitized solar cell made from it has higher efficiency than that constructed from the photoanode comprising of small particles about 10–15 nm in size. The higher efficiency is attributed to the longer diffusion length of electrons because of a better electron transport and penetration of a large amount of \(\hbox {CuCrO}_{2 }\) nanoparticles in the porous structure of \(\hbox {TiO}_{2}\) photoanode. By using the doped \(\hbox {CuCrO}_{2}\) nanoparticles, the efficiency has been increased from 0.027% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\) to 0.033% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Zn and further increased to 0.042% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Mg. The efficiency enhancement by doping is ascribed to the conductivity improvement due to the presence of impurity atoms.