Fig 8 - uploaded by Bo Zhang
Content may be subject to copyright.
XPS spectra of Mn 2p regions of Ca 0.9Àx Yb x La 0.1 MnO 3 (0 £ x £ 0.05) ceramics: (a) x = 0, (b) x = 0.01, (c) x = 0.03, and (d) x = 0.05. Triangle and filled circle indicate the peaks of the Mn 2p spectra attributed to Mn 3+ and Mn 4+ , respectively.
Source publication
The microstructure and thermoelectric properties of Yb-doped Ca0.9−x
Ybx
La0.1 MnO3 (0 ≤ x ≤ 0.05) ceramics prepared by using the Pechini method derived powders have been investigated. X-ray diffraction analysis has shown that all samples exhibit single phase with orthorhombic perovskite structure. All ceramic samples possess high relative densitie...
Contexts in source publication
Context 1
... further reinforce and support the above con- clusion that electrical resistivity depends on the Yb substitution, the average Mn oxidation state was evaluated by XPS measurements. Figure 8 shows the XPS spectrum and the curve-fitting example of Ca 0.9Àx Yb x La 0.1 MnO 3 in the region of Mn 2p core- level peaks. According to the binding energy val- ues, 31 the Mn 2p peaks shown in Fig. 8 , where n i , I i , Ek i , and r i are the number of atoms of element i, the XPS line intensity in terms of peak area, the kinetic energy value corresponding to the line considered, and the cross- section calculated theoretically, respectively. ...
Context 2
... above con- clusion that electrical resistivity depends on the Yb substitution, the average Mn oxidation state was evaluated by XPS measurements. Figure 8 shows the XPS spectrum and the curve-fitting example of Ca 0.9Àx Yb x La 0.1 MnO 3 in the region of Mn 2p core- level peaks. According to the binding energy val- ues, 31 the Mn 2p peaks shown in Fig. 8 , where n i , I i , Ek i , and r i are the number of atoms of element i, the XPS line intensity in terms of peak area, the kinetic energy value corresponding to the line considered, and the cross- section calculated theoretically, respectively. 34,35 As mentioned above, the introduction of a trivalent cation such as Yb 3+ generates Mn ...
Similar publications
Perovskite manganite Ca0.9R0.1MnO3-δ (R = Dy, Yb) ceramics have been synthesized by a traditional solid-state reaction with multicalcination processes. A heterogeneous microstructure including large and small micrometer-sized grains, coherent interfaces, and oxygen defects has been formed with optimized calcination time. The carrier concentration o...
The itinerant electron density (n) near the Fermi level has a close correlation with the physical properties of Sr2FeMoO6. Two series of single-phase Sr(2−y)NayFeMoO6 (y = 0.1, 0.2, 0.3) and Sr(2−y)NayFe(1−x)Mo(1+x)O6 (y = 2x; y = 0.1, 0.2, 0.3) ceramics were specially designed and the itinerant electron density (n) of them can be artificially cont...
Citations
... On the other hand, the effect of bismuth substitution manifest itself by increasing the magnitude of S from 3 μV.K -1 to 67 μV.K -1 (LB0 to LB30) around the transition temperature region. In general, the magnitude of thermoelectric power varies inversely with the carrier concentrations 5,6 . But in the present investigation, due to the same oxidation state of Bi and La, the carrier concentration (Mn 3+ /Mn 4+ : 70/30) is expected to remain same within the experimental limitations. ...
... The highest |S| value at 800 • C has been determined in 0.02 Ce doped samples (-220 μV/K), which is about two times higher than the obtained in 0.10 Ce doped ones (-95 μV/K). Furthermore, it is in the order of those reported for undoped samples (-225 μV/K) [37], and much higher than the rare earth doped materials (-140 to − 160 μV/K) [36,[39][40][41], or even in co-doped ones (-95 to -160 μV/K) [45][46][47]. Besides, the charge carrier concentration can be deduced from the experimental |S| values for high-temperature limit using Heikes formula given as [18,48]: ...
... The highest values from 100 to 800 • C have been obtained in 0.06 Ce doped samples, which display the best combination of ρ and S. In these samples, the highest value has been found at 500 • C (about 0.35 mW/K 2 m), much higher than the obtained in pristine and Sm-doped samples at the same temperature (0.01, and 0.27 mW/K 2 m, respectively) [36]. Moreover, the obtained value at 800 • C (about 0.31 mW/K 2 m) is higher than the doped-CaMnO 3 (between 0.095 and 0.28 mW/K 2 m) [39,41,45], and similar level in co-doped materials (between 0.27 and 0.35 mW/K 2 m) [46,47]. Fig. 6a. ...
... The triplet peaks at 640.50, 641.87, and 643.50 eV for the as-prepared sample were attributed to Mn 2+ , Mn 3+ , and Mn 4+ , respectively. The binding energy peaks of the as-prepared samples agreed with those reported in the literature [60][61][62]. The valence states of the Mn and Co ions in the LSMCo0.35 ...
The effects of substitution at the A- and B sites on the redox performance of a series of lanthanum–strontium–manganese (LSM)-based perovskite oxides (Z = Ni, Co, and Mg) were studied for application in a two-step thermochemical CO2 splitting cycle to produce liquid fuel from synthesis gas using concentrated solar radiation as the proposed energy source and CO2 recovered from the atmosphere as the prospective chemical source. The redox reactivity, stoichiometry of oxygen/CO production, and optimum chemical composition of Ni-, Co-, and Mg-substituted LSM perovskites were investigated to enhance oxygen/CO productivity. Furthermore, the long-term thermal stabilities and thermochemical repeatabilities of the oxides were evaluated and compared with previous data. The valence changes in the constituent ionic species of the perovskite oxides were studied and evaluated by X-ray photoelectron spectroscopy (XPS) for each step of the thermochemical cycle. From the perspectives of high redox reactivity, stoichiometric oxygen/CO production, and thermally stable repeatability in long-term thermochemical cycling, Ni0.20-, Co0.35-, and Mg0.125-substituted La0.7Sr0.3Mn perovskite oxides are the most promising materials among the LSM perovskite oxides for two-step thermochemical CO2 splitting, showing CO productivities of 387–533 μmol/g and time-averaged CO productivities of 12.9–18.0 μmol/(min·g) compared with those of LSM perovskites reported in the literature.
... This greatly affects the possibility of electron hopping to adjacent positions, leading to its higher resistivity. 59 The value of activation energy (E a ) is calculated by the dependence of resistance on temperature, which represents the lowest energy required for the reaction to TA B L E 5 Binding energy of lattice oxygen (OL) and surface adsorbed oxygen (Oad), and the concentration of the lattice oxygen for the YCTO ceramics occur, and is listed in Table 4. The activation energy of YCTO-S is about 0.6 eV, in general agreement with the results reported in the previous work. ...
Y2/3Cu3Ti4O12 ceramic is a novel semiconductor with potential applications in electronic devices. However, its resistance drift and surface structure defects limit the application for negative temperature coefficient thermistor devices. A comparative study of solid‐phase and a Pechini processing of Y2/3Cu3Ti4O12 is presented in this paper, in the particular comparative study of stability. The Pechini method is found to be effective in lowering sintering temperature and improving thermal stability (ΔR/R0 < 0.3％) in comparison with solid‐phase method. The origin of the stability deterioration is related to the oxidation state of Cu ions and the migration of sublattice. The Pechini method overcomes stoichiometric ratio deviations and cation vacancy diffusion, thus reducing metal ion segregation in a continuous high‐temperature environment and thereby showing unique insensitivity to oxygen. The important role of the Pechini method in improving thermal stability is revealed, which is expected to be used in the preparation of high stability electron devices.
... The thermal analysis curves are composed of three steps. The first one starts at 325 K, referring to the decomposition of the organic compounds as an endothermic event [20]. Then, at 345 K, the nitric acid decomposes as presented in Eq. 3 [21]. ...
Calcium manganate (CMO) is a promising n-type semiconductor for thermoelectric applications due to its intrinsic properties. Still, these properties are highly dependent on the processing route used to produce these materials. In this work, properties of the polycrystalline CMO ceramics are reported by studying samples obtained from powders synthesized by a modified Pechini method and sintered at 1543K for 1, 3, 6, 12 and 24 h. Crystallographic parameters of the resulting phases were determined from X-ray diffraction patterns. The ceramics sintered for 6 h has the highest density (94.8%TD), while the CMO-1h sample (sintered only 1 h) presented the lowest density (77.2%TD) due to a large amount of secondary phase and short sintering time. The crystallite sizes of the CMO particles reached 49.2 nm; meanwhile, the grain sizes were in the range from 1.04 to 4.85 ?m. Seebeck coefficient has a negative value, characterizing an n-type material, and its value approached ?350 ?V/K at 873K. The sample sintered for 1 h has the lowest value of thermal conductivity (3.3W/mK), while the ceramics sintered for 3 h reached maximum electrical conductivity value (1830 S/m), both at 873K. In addition, this high conductivity of the ceramics sintered for 3 h contributed to it having the highest ZT value of about 0.039.
... The two Mn 2p peaks (Fig. 8b) corresponding to Mn2P 3/2 and Mn2P 1/2 are centered around 643 eV and 655 eV, respectively. Both the peaks seem to be asymmetric and contains an additional peak which corresponds to the presence of Mn 4? , this confirms the presence of oxygen vacancies in the prepared samples [22]. The reduction of Mn 4? to Mn 3? ions are related to the oxygen vacancies present due to the oxygen vacancies as a consequence of high-temperature sintering. ...
Calcium manganites (CaMnO3) ceramic powders were prepared by sol–gel technique using citric acid as a chelating agent. The polycrystalline powder crystallized in an orthorhombic structure with lattice parameters a = 5.270 Å, b = 7.421 Å and c = 5.231 Å. Dielectric relaxation was observed which can be attributed to Maxwell–Wagner relaxation behavior. The oxidation states of Calcium, Manganese and the presence of oxygen deficiencies in the prepared samples were ascertained by XPS studies.
... They reported that ZT values obtained by chemical route were higher than the ones achieved by solid-state reaction, mainly due to the difference in grain size obtained for each route. Some studies demonstrate that large grain sizes provide improvements in the values of electrical conductivity [24][25][26] . Thus, one of the ways not widely explored by research would be to produce ceramics with larger grains by increasing the sintering time, intending to increase the ZT values. ...
... As the grain size increases, due to effect of sintering time, the electrical conductivity values rise. High grain size values imply into the reduction of grain boundaries, thus the scattering centers are reduced, consequently, the electrical conductivity increases 26,59,60 . The electrical conductivity values obtained in the literature range between 500 S/m 49 and 700 S/m 10 , for ceramics produced by solid-state reaction or chemical method 9 , calcined at 1373 K, and sintering temperature between 1473K and 1523K. ...
Thermoelectric properties of pure polycrystalline CaMnO3 ceramics were significantly enhanced by increasing sintering holding time from 1 to 24 h. The Seebeck coefficient values were reduced while the sintering holding time was increased, and the DC electrical conductivity was enhanced from 255 S/m to 1.748 S/m. This same effect was observed in electronic thermal conductivity, increasing from 5x10-3 to 3.5x10-2W/m K, whereas the lattice thermal conductivity decreased from 5.0 to 4.0 W/m K at 873K. Overall, CaMnO3 ceramic sintered for 24 h demonstrated the best performance, which presented a Figure-of-Merit value of about 0.03. The grain size of the samples ranged from 2.79 µm to 6.45 µm, due to the sintering holding time, directly influencing the high-temperature thermoelectric properties of CaMnO3 ceramics.
... However, pristine MnO compounds exhibit very poor electrical properties [18] due to their low carrier concentration, which can be enhanced by partially substituting calcium with rare earth cations [19]. Among these rare earth cations, one of the most effective, with regard to electrical properties, is Yb 3+ [9,[20][21][22]. ...
... Greater Ag content promotes a slight increase in resistivity, due to higher Ca 2 Mn 2 O 5 secondary phase levels. It is also clear that Ag does not drastically change sample behavior, which was metallic-like for all samples (dρ/dT > 0) in agreement with previous research [9,14,[19][20][21][22]. The lowest value measured for 1 wt.% ...
In this study, Ca0.9Yb0.1MnO3 + x wt.% Ag (with x = 0, 1, 3, 5, and 10) thermoelectric materials were prepared via the classical ceramic method. In spite of the very high sintering temperature (1300 °C), no significant Ag losses were observed following this process. Moreover, Ag addition enhanced cation mobility during sintering due to the formation of a liquid phase. Microstructurally, it was found that Ag decreases porosity; this was confirmed by density measurements. Ag was also found to promote the formation of a Ca2Mn2O5 secondary phase. Despite the presence of this secondary phase, samples with Ag displayed lower electrical resistivity than Ag-free ones, without a drastic decrease in the absolute Seebeck coefficient. The highest thermoelectric performances, which were determined by power factor, were obtained in 1 wt.% Ag samples. These maximum values are slightly higher than the best of those reported in the literature for sintered materials with similar compositions, with the additional advantage of their being obtained using a much shorter sintering procedure.
... The electron doping promoted by Yb substitution, due to the loss of K, enhances the carrier concentration and decreases Seebeck coefficient. On the other hand, these values are higher to the obtained in Yb-doped sintered samples (−90 to −100 µV/ K) [8,[19][20][21], prepared through SPS (−90 µV/K) [18], or in codoped materials (−70 to −120 µV/K) [22][23][24]. However, at 800°C, the maximum values obtained in this work (−230 µV/K) are in the order of undoped samples (−225 µV/K) [17]. ...
... However, at 800°C, the maximum values obtained in this work (−230 µV/K) are in the order of undoped samples (−225 µV/K) [17]. Moreover, they are much higher than the measured in Yb-doped (−140 to −160 µV/K) [8,[19][20][21], or codoped CaMnO 3 sintered materials (−95 to −160 µV/K) [22][23][24]. Table 1 Mean density of Ca 1-x (Yb .5 K .5 ) x MnO 3 samples, as a function of the Yb, and K addition, together with their standard errors, and the relative density taking the theoretical one as 4.705 g/cm 3 [11]. Furthermore, they are still higher than the obtained in samples processed through SPS (−145 µV/K) [18]. ...
CaMnO3-based materials are very attractive among n-type thermoelectric oxides for high-temperature applications when they are appropriately doped. The main drawback of these materials is the cost associated to the necessary rare earth cations. This work aims decreasing the amount of these materials through a partial substitution of Ca²⁺ by an equimolar mixture of K⁺ and Yb³⁺, Ca1-x(K0.5Yb0.5)xMnO3, with x = 0.05, 0.10, 0.15, and 0.20. XRD studies have confirmed that the thermoelectric phase is the major one in all samples. Microstructure has shown the formation of large crystals, and an increasing porosity when the substitution is raised. This evolution has been confirmed through density measurements. Electrical resistivity has been drastically decreased for the 0.10 substituted samples, compared with the 0.05 ones, slightly increasing for higher substitution. On the other hand, absolute Seebeck coefficient and thermal conductivity are lower when the substitution is raised. The best ZT values have been achieved for the 0.10 substituted samples, which are around the typical reported in the literature for higher doping level. These results clearly point out to a decrease of the necessary rare earth dopant content to achieve similar performances in CaMnO3 ceramics, which is of the main economic significance for their industrial production.
... 21 Furthermore, they are similar to the reported for the best codoped CaMnO 3 sintered materials (around 2.3 mΩ.cm). [22][23][24] When evaluating the values at 800°C, the minimum resistivity values measured in this work (4.2 mΩ.cm) are much lower than the pristine CaMnO 3 (35 mΩ.cm), 19 the best measured in Yb-doped sintered materials (7-9 mΩ.cm), 14,15,20 or prepared through SPS (8 mΩ.cm). 21 On the other hand, they are comparable to the best reported results in codoped CaMnO 3 (between 3.6 and 6.5 mΩ.cm). ...
... 21 On the other hand, they are comparable to the best reported results in codoped CaMnO 3 (between 3.6 and 6.5 mΩ.cm). [22][23][24] From these data, it is clear that attritionmilled precursors are very useful to obtain samples with very low electrical resistivity due to the microstructural improvements induced using small particle size precursors. Figure 7 displays the variation in the Seebeck coefficient as a function of temperature for the different samples. ...
... On the other hand, the values measured in this work at room temperature are comparable to the obtained in Yb-doped sintered samples (À90 to À100 lV/K), 14,20 prepared using SPS (À90 lV/K), 21 or in codoped materials (À70 to À120 lV/K). [22][23][24] When comparing the values at high temperature (800°C), the values measured in this work (À160 lV/K) are still lower than in the pure samples (À225 lV/K), 19 but higher than the measured in Yb-doped sintered samples (À140 to À150 lV/ K), 14,20 or sintered by SPS (À145 lV/K). 21 Moreover, they are higher than most of the reported values for codoped CaMnO 3 materials (À95 to À160 lV/K). ...
Ca0.9Yb0.1MnO3 thermoelectric materials have been prepared, through a classical solid state sintering method, from attrition, and ball milled precursors. After calcination step, microstructural observations have shown that attrition milled precursors possess much smaller particle sizes than the obtained by ball milling. Smaller precursors sizes lead to higher reactivity, producing higher density, hardness, and thermoelectric phase content in the sintered materials. The thermoelectric properties reflect the microstructural features, decreasing electrical resistivity in the attrition milling prepared samples without a drastic decrease of Seebeck coefficient. As a consequence, power factor values are higher than the obtained in the classical solid state method samples. Moreover, the highest power factor values at 800 °C are much higher than the best results obtained in this CaMnO3 family. As a result, it has been found that it is possible to tailor the thermoelectric properties of Ca0.9Yb0.1MnO3 ceramics by designing the appropriate preparation procedure while keeping in mind its industrial scalability. This article is protected by copyright. All rights reserved.
