Low-temperature preparation and physical characterization of doped BaCeO₃ nanoparticles by chemical precipitation

Abstract

Background

In this work, the nanoparticles of pure BaCe_1−xM _x O_3−δ (where M = Gd or Sm and x = 0, 0.10, or 0.20) were synthesized by the simple chemical precipitation method. The prepared materials were calcined at 300°C, 450°C, and 600°C for 2 h each to obtain phase-pure compounds. The samples were characterized by thermogravimetry/differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDAX) analysis, Fourier transform infrared (FTIR), particle size analysis, and scanning electron microscopy.

Results

TGA/DTA results have shown that phase-pure BaCeO₃ materials can be formed only above 500°C. The crystalline structure of parent and doped BaCeO₃ was found to be orthorhombic. EDAX analysis has shown the atomic percentage of elements present in the Gd- and Sm-doped BaCeO₃ samples. FTIR studies have shown the presence of Ce-O in doped BaCeO₃ nanoparticles.

Conclusions

Doped BaCeO₃ may be used as an electrolyte for solid oxide fuel cell applications.

Background

Complex cerium oxides with perovskite-related structures are promising ceramic materials for application in hydrogen sensors, electro-catalytic reactors for hydrogen separation, and also as electrolytes in solid oxide fuel cells operating on hydrocarbon fuels. BaCe_1−xM _x O_3−δ (M = trivalent ion such as Y, Yb, Nd, Gd, Sm, and so on) has been studied as a high proton conducting oxide operated at 400°C to 600°C, which is expected as an electrolyte of solid oxide fuel cells [1–3], hydrogen separation membranes, hydrogen gas sensors [4, 5], and so on. Recently, these materials were also found to be of broad interest as catalysts for oxidation reactions because of their ability to conduct oxygen and to support significant variations in oxygen contents [6]. As well known, in the next generation of energy devices such as solid oxide fuel cells (SOFC), there is considerable emphasis on moving to lower temperature of operation. One of the important problems in this direction will be addressed to find suitable materials that operate well at lower temperatures. Good progress can be achieved using perovskites such as doped BaCeO₃. For this reason, BaCeO₃ phases doped by different dopants seem to be perspective materials for future application. These materials are usually formed by a conventional ceramic process consisting of calcining mixtures of the respective oxides and carbonates at temperatures >1,200°C followed by sintering of the powder compacts at temperatures of 1,400°C to 1,600°C [7]. The solid-state reaction is a diffusion-controlled process which requires intimacy of reacting species and a uniform distribution of each species to obtain a completely reacted and uniform product. Since the starting materials generally have a large particle size, this approach frequently needs repeated mixing and extended heating at high temperature in order to generate a homogeneous and single-phase material [8]. The mechanical mixing process will very likely introduce contaminants from abrasive materials [9]. Moreover, prolonged calcination promotes crystallite growth, which is undesirable in the fabrication of dense fine-grained ceramics which undoubtedly possess better electrical properties. In order to overcome all these disadvantages, wet chemical routes like coprecipitation of metal ions may be a promising alternative. The principal advantages of starting from a solution are better homogeneity and improved reactivity. The necessary solid-state reactions proceed more rapidly and at lower temperatures. As a consequence, the desired product can be obtained with a smaller particle size and greater reactivity. To date, only a few wet chemical processes were attempted to prepare such materials. Based on the fact that doped BaCeO₃ phases have good perspective as proton conductors, we decided to prepare BaCeO₃ (BC) with compositions such as BaCe_0.9Gd_0.1O_3−δ and BaCe_0.8Sm_0.2O_3−δ systems (abbreviated as BCGO and BCSO) and characterize them. In this research work, we focus our attention on the synthesis of the above ceramic materials by the chemical precipitation process. The main purpose of this work is to prepare Gd/Sm-doped BaCeO₃ by the chemical precipitation method in the presence of sodium hydroxide (precipitant) and polyvinyl pyrrolidone (PVP, surfactant) and to study the basic structural and particulate properties of the samples.

Methods

Preparation of BaCe_1−xGd _x /Sm _x O_3−δ(where x= 0, 0.10, or 0.20) nanoparticles by chemical precipitation process

In the typical experiment, the aqueous solution containing a known concentration of barium nitrate, cerium nitrate, and gadolinium nitrate/samarium nitrate (as basic materials) and sodium hydroxide (as precipitator material) was prepared in distilled water. Gadolinium nitrate/samarium nitrate was prepared by dissolving the required quantity of Gd₂O₃/Sm₂O₃ in HNO₃. Initially, the precipitating solution (sodium hydroxide) was mixed with 2 ml of 10% PVP (as surfactant material). To this mixture, Ba(NO₃)₂, Ce(NO₃)₃, and Gd(NO₃)₃/Sm(NO₃)₃ solutions were consequently added one by one dropwise. They were mixed perfectly by a magnetic stirring apparatus (1,000 rpm) at room temperature for 1 h. The pH was maintained at greater than 9 throughout the experiment by the addition of alkali. The resultant yellow-colored precipitate ((Ba(OH)₂ + Ce(OH)₄ + Gd(OH)₃ with PVP) or (Ba(OH)₂ + Ce(OH)₄ + Gd(OH)₃ with PVP)) was filtered and then washed with deionized water and ethanol five to ten times. The product was dried at 50°C to 100°C for 24 h. The resultant material was calcined at 300°C, 450°C, and 600°C for 2 h each. During calcination, the surfactant was removed, and phase-pure, yellow-colored BaCe_1−xGd _x O_3−δ or BaCe_1−xSm _x O_3−δ was formed. To study the crystallographic parameters of undoped BaCeO₃, parent BaCeO₃ was also prepared using the same process without the addition of Gd(NO₃)₃/Sm(NO₃)₃. The amount of precursor materials used for the preparation of BaCe_1−xGd _x /Sm _x O_3−δ (where x = 0, 0.10, or 0.20) nanoparticles is indicated in Table 1. Figure 1 shows a schematic of the synthesis of BaCe_1−xGd _x /Sm _x O_3−δ (where x = 0, 0.10, or 0.20) by chemical precipitation. The main reactions involved in the preparation of parent BaCeO₃, BaCe_0.9Gd_0.1O_3−δ, and BaCe_0.8Sm_0.2O_3−δ during the experimental procedure can be written briefly as follows:

Figure 1

The synthesis of BaCe _{1− x} Gd _x /Sm _x O _{3− δ} (where x = 0, 0.10, or 0.20) nanoparticles by chemical precipitation.

Table 1 Amount of precursor materials (dissolved in 100 ml of water) used to prepare BaCe _{1− x} Gd _x /Sm _x O _{3− δ} nanoparticles

Reaction mechanism involved in the preparation of parent BaCeO₃:

$$\begin{array}{l}0.3\mathrm{NaOH}\to 0.3{\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+0.3{\mathrm{OH}}^{-}\left(\mathrm{aq}\right),\\ 0.05\mathrm{Ba}{\left(\mathrm{NO}\right)}_3\to 0.05{\mathrm{Ba}}^{2+}\left(\mathrm{aq}\right)\\ +0.05{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)}0.05\mathrm{Ce}{\left({\mathrm{NO}}_3\right)}_3.6{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ \to 0.05{\mathrm{Ce}}^{3+}\left(\mathrm{aq}\right)+0.15{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)}\\ +6{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{aq}\right)},\\ 0.05{\mathrm{Ba}}^{2+}\left(\mathrm{aq}\right)+0.05{\mathrm{Ce}}^{3+}\left(\mathrm{aq}\right)+0.3{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)\\ +x{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{aq}\right)}\to 0.05\mathrm{Ba}{\left(\mathrm{OH}\right)}_2.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow \\ +0.05\mathrm{Ce}{\left(\mathrm{OH}\right)}_4.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow ,\\ {50}^{\mathrm{°}}\mathrm{C}-{100}^{\mathrm{°}}\mathrm{C}0.05\mathrm{Ba}{\left(\mathrm{OH}\right)}_2.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ +0.05\mathrm{Ce}{\left(\mathrm{OH}\right)}_4.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\to 0.05\mathrm{Ba}{\left(\mathrm{OH}\right)}_{2\left(S\right)}\\ +0.05\mathrm{Ce}{\left(\mathrm{OH}\right)}_{4\left(s\right)}+x{\mathrm{H}}_2{\mathrm{O}}_{\left(g\right)}\uparrow ,\\ \begin{array}{l}{600}^{\mathrm{°}}\mathrm{C}0.05\mathrm{Ba}{\left(\mathrm{OH}\right)}_{2\left(S\right)}+0.05\mathrm{Ce}{\left(\mathrm{OH}\right)}_{4\left(s\right)3}\\ \to 0.05{\mathrm{BaCeO}}_3+x{\mathrm{H}}_2{\mathrm{O}}_{\left(g\right)}\uparrow \end{array}\end{array}$$

Reaction mechanism involved in the preparation of BaCe_0.9Gd_0.1O_3−δ:

$$\begin{array}{l}5.9\mathrm{NaOH}\to 5.9{\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+5.9{\mathrm{OH}}^{-}\left(\mathrm{aq}\right),\\ \mathrm{Ba}{\left(\mathrm{NO}\right)}_3\to {\mathrm{Ba}}^{2+}\left(\mathrm{aq}\right)\\ +{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)}0.9\mathrm{Ce}{\left({\mathrm{NO}}_3\right)}_3.6{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ \to 0.9{\mathrm{Ce}}^{3+}\left(\mathrm{aq}\right)+2.7{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)}+6{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{aq}\right)},\\ 0.1\mathrm{Gd}{\left({\mathrm{NO}}_3\right)}_3\to 0.1{\mathrm{Gd}}^{3+}\left(\mathrm{aq}\right)+0.3{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)},\\ {\mathrm{Ba}}^{2+}\left(\mathrm{aq}\right)+0.9{\mathrm{Ce}}^{3+}\left(\mathrm{aq}\right)+0.1{\mathrm{Gd}}^{3+}\\ +5.9{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)+x{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{aq}\right)}\\ \to \mathrm{Ba}{\left(\mathrm{OH}\right)}_2.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow +0.9\mathrm{Ce}{\left(\mathrm{OH}\right)}_4.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow \\ +0.1\mathrm{Gd}{\left(\mathrm{OH}\right)}_3.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow ,\\ {50}^{\mathrm{°}}\mathrm{C}-{100}^{\mathrm{°}}\mathrm{C}\mathrm{Ba}{\left(\mathrm{OH}\right)}_2.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ +0.9\mathrm{Ce}{\left(\mathrm{OH}\right)}_4.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}+0.1\mathrm{Gd}{\left(\mathrm{OH}\right)}_3.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ \to \mathrm{Ba}{\left(\mathrm{OH}\right)}_{2\left(S\right)}+0.9\mathrm{Ce}{\left(\mathrm{OH}\right)}_{4\left(s\right)}+0.1\mathrm{Gd}{\left(\mathrm{OH}\right)}_{3\left(s\right)}\\ +x{\mathrm{H}}_2{\mathrm{O}}_{\left(g\right)}\uparrow ,\\ {600}^{\mathrm{°}}\mathrm{C}\mathrm{Ba}{\left(\mathrm{OH}\right)}_{2\left(S\right)}+0.9\mathrm{Ce}{\left(\mathrm{OH}\right)}_{4\left(s\right)}\\ +0.1\mathrm{Gd}{\left(\mathrm{OH}\right)}_3\to {\mathrm{BaCe}}_{0.9}{\mathrm{Gd}}_{0.1}{\mathrm{O}}_{3-\delta }+x{\mathrm{H}}_2{\mathrm{O}}_{\left(g\right)}\uparrow \end{array}$$

Reaction mechanism involved in the preparation of BaCe_0.8Sm_0.2O_3−δ:

$$\begin{array}{l}5.8\mathrm{NaOH}\to 5.8{\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+5.8{\mathrm{OH}}^{-}\left(\mathrm{aq}\right),\\ \mathrm{Ba}{\left(\mathrm{NO}\right)}_3\to {\mathrm{Ba}}^{2+}\left(\mathrm{aq}\right)+{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)}0.8\mathrm{Ce}{\left({\mathrm{NO}}_3\right)}_3.6{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ \to 0.8{\mathrm{Ce}}^{3+}\left(\mathrm{aq}\right)+2.4{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)}+6{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{aq}\right)},\\ 0.2\mathrm{Sm}{\left({\mathrm{NO}}_3\right)}_3\to 0.2{\mathrm{Sm}}^{3+}\left(\mathrm{aq}\right)+0.6{\mathrm{NO}}_3{-}_{\left(\mathrm{aq}\right)},\\ {\mathrm{Ba}}^{2+}\left(\mathrm{aq}\right)+0.8{\mathrm{Ce}}^{3+}\left(\mathrm{aq}\right)+0.1{\mathrm{Sm}}^{3+}+5.8{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)\\ +x{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{aq}\right)}\to \mathrm{Ba}{\left(\mathrm{OH}\right)}_2.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow \\ +0.8\mathrm{Ce}{\left(\mathrm{OH}\right)}_4.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow +0.2\mathrm{Sm}{\left(\mathrm{OH}\right)}_3.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\downarrow ,\\ {50}^{\mathrm{°}}\mathrm{C}–{100}^{\mathrm{°}}\mathrm{C}\mathrm{Ba}{\left(\mathrm{OH}\right)}_2.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ +0.8\mathrm{Ce}{\left(\mathrm{OH}\right)}_4.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}+0.2\mathrm{Sm}{\left(\mathrm{OH}\right)}_3.x{\mathrm{H}}_2{\mathrm{O}}_{\left(s\right)}\\ \to \mathrm{Ba}{\left(\mathrm{OH}\right)}_{2\left(S\right)}+0.8\mathrm{Ce}{\left(\mathrm{OH}\right)}_{4\left(s\right)}+0.2\mathrm{Sm}{\left(\mathrm{OH}\right)}_{3\left(s\right)}\\ +x{\mathrm{H}}_2{\mathrm{O}}_{\left(g\right)}\uparrow ,\\ {600}^{\mathrm{°}}\mathrm{C}\mathrm{Ba}{\left(\mathrm{OH}\right)}_{2\left(S\right)}+0.8\mathrm{Ce}{\left(\mathrm{OH}\right)}_{4\left(s\right)}\\ +0.2\mathrm{Sm}{\left(\mathrm{OH}\right)}_3\to {\mathrm{BaCe}}_{0.9}{\mathrm{Sm}}_{0.2}{\mathrm{O}}_{3-\delta }+x{\mathrm{H}}_2{\mathrm{O}}_{\left(g\right)}\uparrow \end{array}$$

Thermal analysis of the precursor material was performed with SI EXSTAR 6000 TG/DTA 6300 instrument (Hitachi, Tokyo, Japan) between 25°C and 700°C in nitrogen atmosphere. The powder X-ray diffraction (XRD) studies were carried out using a Shimadzu XRD6000 X-ray diffractometer (Shimadzu, Kyoto, Japan) at a scan speed of 5°/min using CuKα radiation. The lattice parameters were calculated by least square fitting method using DOS computer programming. The theoretical density of the powders was calculated with the obtained XRD data. Energy-dispersive X-ray spectroscopy (EDAX) analysis was performed with a JEOL model JSM-6360 (JEOL Ltd., Tokyo, Japan) to find out the percentage of elements present in the samples. The crystallite sizes of the powder were calculated using Scherrer's formula. A Bruker IFS 66 V FTIR spectrometer (Bruker AXS, Madison, WI, USA) was employed to record the Fourier transform infrared (FTIR) spectra of doped BaCeO₃ powder in the range of 4,000 to 400 cm⁻¹. The crystallite sizes of the ceramic powders were calculated using Scherrer's formula. The particle size of the powder was measured with a Malvern particle size analyzer (Malvern Instruments, Worcestershire, UK) using triple-distilled water as medium. The surface morphology of the particles was studied using JEOL model JSM-6360 scanning electron microscope.

Results and discussion

Thermogravimetry/differential thermal analysis of precursor materials

The TGA/DTA spectra obtained with the precursor materials ((Ba(OH)₂ + Ce(OH)₄ + Gd(OH)₃ + PVP) and (Ba(OH)₂ + Ce(OH)₄ + Sm(OH)₃ + PVP)) are indicated in Figures 2 and 3. The DTA peaks closely correspond to the weight changes observed on the TGA curves. From Figure 2, the total weight loss at the temperature of 25°C to 700°C was found to be 10.0%. From the curve, it is understood that the weight loss begins to appear from the initial stage. The weight loss of about 3.6% is found at around 100°C, which is due to the removal of water molecule from the water sample. Then, the total weight loss of 5.7% is found at around 250°C, which is attributed to the removal of organics present in the sample. This is confirmed with an exothermic peak around 250°C in the DTA curve. The further weight loss present in the sample until 700°C is due to the decomposition of remaining carbon/nitrogen-based compounds from the sample.

Figure 2

TGA/DTA spectrum obtained with the precursor material (Ba(OH) ₂ + Ce(OH) ₄ + Gd(OH) ₃ + PVP).

Figure 3

TGA/DTA spectrum obtained with the precursor material (Ba(OH) ₂ + Ce(OH) ₄ + Sm(OH) ₃ + PVP).

From Figure 3, the total weight loss at the temperature of 25°C to 500°C was about 12%. This reduction in weight is attributed to the removal of water and other carbon and nitrogen oxides evolved from the sample during gradual heat treatment. From the curve, it is clear that the weight loss at 100°C is around 4.7%, which is attributed to the removal of water molecule from the sample. A strong exothermic peak found at around 258°C in the DTA curve indicates the start of the removal of carbon- and nitrogen-based compounds from the sample. At around 700°C, the weight loss is stable, which indicates the formation of phase-pure doped BaCeO₃.

Structural determination of doped BaCeO₃ particles by powder X-ray diffraction

It has been reported that the XRD patterns of rare-earth-oxide-doped BaCeO₃ is indexed to the orthorhombic crystal system with space group Pnma[10]. By using neutron diffraction measurements at high temperatures, Knight reported that crystal structure of BaCeO₃ at room temperature was orthorhombic distorted perovskite with space group of Pnma (no. 62) [11]. He also reported three types of structural phase transitions: from primitive orthorhombic perovskite to body-centered one with space group of Imma (no. 74), from the Imma to rhombohedrally distorted one with space group of R3c (no. 167), and from the R3c to cubic one with space group of Pm3m (no. 227) at 290°C, 400°C, and 900°C, respectively. Knight also investigated the structural phase transition of BaCe_1−xM _x O_3−δ by neutron diffraction measurements. Chen and Gulin synthesized BaCe_1−xGd _x O_3−δ (0.05 ≤ x ≤ 0.20) by a microemulsion method and studied their structural properties. They reported that the structure of BaCeO₃ was found to be orthorhombic [12]. Gorbova et al. [13] have studied the structural and electrical properties of samarium-doped barium cerate (BaCe_1−xSm _x O_3−δ, with x = 0 to 0.2) prepared by solid-state reaction method. They found that according to the XRD analysis at 0 ≤ x ≤ 0.2, the formed continuous series of BaCe_1−xSm _x O_3−δ solid solutions have the structure of cubic perovskite with orthorhombic distortions. Matskevich et al. [11] have studied the structural properties of BaCe_0.9Ga_0.1O_3−δ, and they reported the structure as orthorhombic with unit cell parameters a = 6. 23413 Å, b = 6.21236 Å, and c = 8.77180 Å. The lattice parameter of Ba(Ce_0.8Zr_0.2)_0.95Yb_0.05O_2.975 oxide prepared by Pechini method and calcined at 1,400°C was estimated and found to be a = 8.737 Å, b = 6.182 Å, and c = 6.197 Å (V = 334.713 ų) [14].

In this work, the structural properties of the parent BaCeO₃, BaCe_0.9Gd_0.1O_3−δ, and BaCe_0.8Sm_0.2O_3−δ synthesized by chemical precipitation technique are investigated by XRD observation, which are demonstrated in Figure 4. The XRD patterns of the undoped and doped BaCeO₃ match with the standard data for BaCeO₃ (JCPDS card no. 22–74), indicating an orthorhombic crystal structure. In the XRD pattern of BaCeO₃, one additional peak was observed at 2θ = 23.8°, which may be due to the presence of impurity in the sample. However, in the doped BaCeO₃ sample, no other peak corresponding to any impurity was observed. The diffraction patterns of the BaCe_0.9Gd_0.1O_3−δ and BaCe_0.8Sm_0.2O_3−δ are similar to that of reported BaCeO₃ except for slight shifts in the diffraction angles. However, the presence of additional peaks in the parent BaCeO₃ matched well with the standard data reported in JCPDS card no. 22–74. The lattice parameters are calculated from 2θ values in the X-ray diffraction patterns. The powder XRD data obtained with BaCeO₃, BaCe_0.9Gd_0.1O_3−δ, and BaCe_0.8Sm_0.2O_3−δ are reported in Tables 2, 3, 4, 5, 6, and 7. The unit cell volume, crystallite size, and theoretical density values are calculated for these samples, and the values were found to be similar to each other. The theoretical density calculated from the XRD data for the BaCeO₃ powder was reported as 5.96 g/cm³. Also, it is reported that the crystallite size calculated for BaCeO₃ powder was lower than the actual grain size measured by sophisticated techniques like scanning electron microscopy (SEM) [15]. The reported data on the crystallographic properties for BaCeO₃ agree with the parent and doped BaCeO₃ reported in this paper.

Figure 4

XRD patterns. Obtained with calcined (a) BC, (b) BCGO, and (c) BCSO powders prepared by chemical precipitation method.

Table 2 XRD data obtained with parent BC powder

Table 3 Crystal structure and parameters obtained with BC powder

Table 4 XRD data obtained with BCGO powder

Table 5 Crystal structure and parameters obtained with BCGO powder

Table 6 XRD data obtained with BCSO powder

Table 7 Crystal structure and parameters obtained with BCSO powder

Chemical composition of the of doped BaCeO₃ powders

The EDAX spectra obtained with BCGO and BCSO powders are reported in Figure 5. The chemical composition data derived for the samples from the EDAX analysis is indicated in Table 8. From the data, it was found that the elements were present as per the requirement.

Figure 5

EDAX spectra obtained with calcined (a) BCGO and (b) BCSO powders prepared by chemical precipitation.

Table 8 Chemical composition data obtained with BCGO and BCSO powders by EDAX analysis

FTIR spectroscopic studies of doped BaCeO₃ powders

Figures 6 and 7 show the FTIR spectra obtained with BCGO and BCSO powders prepared by chemical precipitation method. FTIR measurements were done using KBr method at room temperature. The wide absorption bands that appeared at 3,428 cm⁻¹ in BCGO and 3,457 cm⁻¹ in BCSO are attributed to the stretching vibration of water H-O bond (moisture) [16]. According to standard IR spectra, peaks that appeared at 1,391 and 511 cm⁻¹ in BCGO and 1,359 and 541 cm⁻¹ in BCSO, as well as the shoulder peaks that appeared around 1,500 to 1,700 cm⁻¹ in both samples, are attributed to the Ce-O in the sample as reported [17]. Also, the bands that appeared at around 2,500 cm⁻¹ in both samples are attributed to the presence of CO₂ in the sample [18]. The bands in the region 1,000 to 650 cm⁻¹ have been assigned to the stretching modes, and the region 650 to 450 cm⁻¹ contains bridging stretching modes in both samples [19].

Figure 6

FTIR spectrum obtained with calcined BCGO powder prepared by chemical precipitation method.

Figure 7

FTIR spectrum obtained with calcined BCSO powder prepared by chemical precipitation method.

Particulate properties obtained with BCGO/BCSO powders

The prepared doped barium cerate particles were subjected to particle size measurements using a Malvern particle size analyzer with triple-distilled water as medium. For all the measurement, 0.20 g of sample was sonicated in 200 ml of triple-distilled water for about 5 min, and after that, the sample was subjected to particle size analysis. The particle size distribution curves obtained with BCGO and BCSO samples prepared by chemical precipitation method are shown in Figures 8, 9, 10 and 11, respectively. The particle characteristics are indicated in Tables 9, 10, 11, and 12, respectively. From Figures 10 and 11 and the particle characteristic data (Tables 11 and 12), it was understood that the average particle size of BCSO powder prepared by chemical precipitation method is found to be around the range of 110.4 to 132.1 nm, which is higher than the particle size data obtained for other samples. The presence of higher particle size may be due to the agglomeration of particles at high-temperature treatment [20].

Figure 8

Particle size distribution patterns (based on intensity) obtained with BCGO powder prepared by chemical precipitation. For the different trials (a, b, c) carried out for particle size analysis.

Figure 9

Particle size distribution patterns (based on volume) obtained with BCGO powder prepared by chemical precipitation. For the different trials (a, b, c) carried out for particle size analysis.

Figure 10

Particle size distribution patterns (based on intensity) obtained with BCSO powder prepared by chemical precipitation. For the different trials (a, b, c, d) carried out for particle size analysis. The colored lines indicate the measurement recorded details.

Figure 11

Particle size distribution patterns (based on volume) obtained with BCSO powder prepared by chemical precipitation. For the different trials (a, b, c, d) carried out for particle size analysis. The colored lines indicate the measurement recorded details.

Table 9 Particle characteristic data (based on intensity) obtained with BCGO powder prepared by chemical precipitation method

Table 10 Particle characteristic data (based on volume) obtained with BCGO powder prepared by chemical precipitation method (with 2 ml PVP)

Table 11 Particle characteristic data (based on intensity) obtained with BCSO powder prepared by chemical precipitation method

Table 12 Particle characteristic data (based on volume) obtained with BCSO powder prepared by chemical precipitation method

SEM studies of doped BaCeO₃ powders

The SEM photographs obtained with BCGO and BCSO are shown in Figure 12. From the micrographs (Figure 12a,b), it was noticed that the surface of Gd-doped BaCeO₃ was not smooth. Bigger grains were also seen. The grain size varied from the lower side to higher side. The presence of bigger particles in the sample (BaCe_0.9Gd_0.1O_2−δ) is due to the combination of few particles together at high temperature. The average grain size of BaCe_0.9Gd_0.1O_2−δ was found to be around 70 nm. From Figure 12c,d, it was understood that different size of particles were present in the BaCe_0.8Sm_0.2O_2−δ powder. The surface was rough. The grain size was found to be in the range of 50 to 70 nm in BaCe_0.8Sm_0.2O_2−δ powder. The presence of large particles (>100 nm) may be due to the agglomeration of particles during high-temperature treatment.

Figure 12

SEM photographs obtained with calcined (a, b) BCGO and (c, d) BCSO powder.

Experimental

This research paper describes the preparation of BaCe_1−xM _x O_3−δ (where M = Gd or Sm and x = 0, 0.10, or 0.20) by a simple low-temperature chemical precipitation method. The precursor materials used in this research work were barium nitrate, cerium nitrate, and gadolinium nitrate/samarium nitrate (as basic materials); sodium hydroxide (as a precipitator material); and polyvinyl pyrrolidone (as surfactant). In a typical experiment, the aqueous solution containing Ba²⁺, Ce³⁺, and Gd³⁺/Sm³⁺ ions was mixed with the solution of alkali in a magnetic stirrer, and then the required percentage of surfactant was added. The formed hydroxides of Ba, Ce, and Gd/Sm were washed with water and ethyl alcohol, dried at 50°C to 100°C for 24 h, and finally, heat-treated at 300°C, 450°C, and 600°C for 2 h each to get phase-pure products. Suitable reaction mechanisms were proposed for the preparation of BaCeO₃-based materials.

Conclusions

The preparation of phase-pure BCGO and BCSO nanoparticles using barium nitrate, cerium nitrate hexahydrate, Gd₂O₃, Sm₂O₃, nitric acid, sodium hydroxide, and surfactant (PVP) by simple wet chemical method (chemical precipitation method) is dealt with. The TGA/DTA data revealed the removal of moisture and other organics from the precursor materials. Also, the TGA/DTA data helped to find out the suitable calcination temperature to prepare phase-pure compound. The powder XRD data obtained with parent and doped BaCeO₃ powder is in good agreement with the standard reported JCPDS data. The crystalline structure of BaCeO₃ is orthorhombic. The EDAX data confirmed the presence of required elements in both samples. From the FTIR data, it is understood that the characteristic peak of Ce-O is present in both samples. The particulate properties of both samples suggest that the particles are present in nanometer range. The presence of nanosized particles in both samples is also confirmed with SEM data. After measuring the protonic conductivity of doped BaCeO₃ nanomaterials, these materials may be utilized for application in SOFCs as electrolyte materials.

Authors’ information

JJK and DR are research scholars at the Department of Chemistry, Karunya University, Coimbatore, India. They are working in the synthesis and characterization of novel materials applicable for low-temperature solid oxide fuel cells.

ASN is working as an associate professor and admissions officer at the Department of Chemistry, Karunya University, Coimbatore, India. He is working in the field of nanoparticles for application in electrochemical power sources since 1996. At present, four research scholars are working for their PhD degree under his guidance.