Structural studies of evolution of solid solutions of BaTiO3 doped with Er3+ (solid-state reaction method)

Miguel Pérez-Labraa,*, Francisco R. Barrientos-Hernándeza, Juan P. Hernández-Laraa, José A. Romero-Serranob, Martín Reyes-Péreza, Víctor E. Reyes-Cruza, Julio C. Juárez-Tapiaa, Gustavo Urbano-Reyesa

aAcademic Area of Earth Sciences and Materials, Autonomous University of Hidalgo State. Road Pachuca- Tulancingo Km 4.5 Mineral de la Reforma, Zip Code 42184, Hidalgo México

bMetallurgy and Materials Department, ESIQIE-IPN. UPALM, Zacatenco, Zip Code 07738, Ciudad de México, México

(*Corresponding author:



Erbium doped BaTiO3 compositions were synthetized using the conventional solid-state method in air atmosphere, according to the general formula Ba1-xErxTi1-x/4O3 and x = 0.0, 0.003, 0.005, 0.01, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35 Er3+ (wt. %). BaTiO3:Er3+ were prepared using barium carbonate [BaCO3], titanium oxide [TiO2] and erbium oxide [Er2O3] as precursors. The powders were decarbonated at 900 °C for 12 h and sintered at 1400 °C for 12 h. The structural evolution of solid solutions was monitored by X-ray diffraction, Raman spectroscopy, Infrared spectroscopy and scanning electron microscopy. The results showed that the crystal phase of the particles obtained was predominately tetragonal BaTiO3. A secondary phase identified as a pyrochlore (Er2Ti2O7) was found when the Er3+ content was higher than 0.05 wt. %. The solubility limit of Er3+ in the crystal structure of BaTiO3 was reached when x was = 0.05. The results obtained by MEB-EDS indicated the incorporation of erbium in the crystalline structure of BaTiO3. The IR results showed no absorption bands contamination of O-H group into the products.



Estudios de evolución estructural de soluciones solidas de BaTiO3 dopadas con Er3+ (método de reacción en estado sólido). Se sintetizaron composiciones de BaTiO3 dopadas con erbio empleando el método convencional de reacción en estado sólido en atmosfera de aire, de acuerdo a la formula general Ba1-xErxTi1-x/4O3 y x = 0,0; 0,003; 0,005; 0,01; 0,05; 0,1; 0,15; 0,20; 0,25; 0,30; 0,35 Er3+ (% peso). Las muestras de BaTiO3 dopadas con Er3+ fueron preparadas usando carbonato de bario [BaCO3], óxido de titanio [TiO2] y óxido de erbio [Er2O3] como precursores. Los polvos fueron decarbonatados a 900 °C por 12 h y sinterizados a 1400 °C por 12 h. La evolución estructural de las soluciones sólidas fue monitoreada por difracción de rayos X (DRX), espectroscopia Raman (ER), espectroscopia de infrarrojo (EI) y microscopía electrónica de barrido (MEB-EDS). Los resultados mostraron que la fase cristalina de las partículas obtenidas fue BaTiO3 predominantemente tetragonal. Se encontró una fase secundaria identificada como pirocloro (Er2Ti2O7) cuando el contenido de Er3+ en las muestras fue mayor que 0,05 % peso. El límite de solubilidad de Er3+ en la estructura cristalina del BaTiO3 se alcanzó cuando x fue = 0,05. Los resultados obtenidos por MEB-EDS indicaron la incorporación de erbio en la estructura cristalina del BaTiO3. Los resultados de EI no mostraron bandas de contaminación de grupos O-H en los productos obtenidos.


Submitted: 28 November 2017; Accepted: 20 February 2018; Available On-line: 02 October 2018

Citation/Citar como: Pérez-Labra, M.; Barrientos-Hernández, F.R.; Hernández-Lara, J.P.; Romero-Serrano, J.A.; Reyes-Pérez, M.; Reyes-Cruz, V.E.; Juárez-Tapia, J.C.; Urbano-Reyes, G. (2018). “Structural studies of evolution of solid solutions of BaTiO3 doped with Er3+ (solid-state reaction method)”. Rev. Metal. 54(4): e129.

KEYWORDS: BaTiO3; Doping; Er3+; Sintering

PALABRAS CLAVE: BaTiO3; Dopaje; Er3+; Sinterización

ORCID ID: Miguel Pérez-Labra (; Francisco R. Barrientos-Hernández (; Juan P. Hernández-Lara (; José A. Romero-Serrano (; Martín Reyes-Perez (; Víctor E. Reyes-Cruz (; Julio C. Juárez-Tapia (; Gustavo Urbano-Reyes (

Copyright: © 2018 CSIC. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License.




Barium titanate (BaTiO3) is a ferro-electric material that can be formulated in a large number of systems and solid solutions that provide a wide range of various applications. The ferro-electric (tetragonal) phase gets converted into para-electric (cubic) phase at the Curie temperature (Tc) at ∼ 120 °C for single-crystals. Its structure type perovskite has the capability to host ions of different sizes; so, an important number of distinct dopants can be accommodated in the BaTiO3 lattice, which makes BaTiO3 semi-conducting (Vijatovic´ et al., 2010). The doping process of BaTiO3-based ceramics is of great value in the production of electric and electronic devices (multilayer capacitors, piezoelectric transducers sensors with positive temperature coefficient of resistivity etc.) (Jaffe, 1971; Moulson and Herbert, 2003). The BaTiO3 doping process with rare earth ions has been of interest to many researchers, who have found significant improvements in its electrical properties (Pinceloup et al., 1999; Durán et al., 2001; Hwang et al., 2004; Zhao et al., 2006; Hao et al., 2011; Zhang et al., 2011; Yan-Xia et al., 2012; Zhang and Hao, 2013). Specifically, erbium, (trivalent lanthanide element) has been mainly researched as a dopant in optical fiber amplifiers (Tsur et al., 2001; Yongping et al., 2007; Markom et al., 2017), where it showed excellent properties. As a dopant in BaTiO3, nanoparticles have been synthesized using the hydrothermal method, generating a stable cubic phase below 30 nm in size (Garrido-Hernández et al., 2014). The structure of BaTiO3 is of great importance, because its properties depend on its crystallographic phase. The cubic phase has para-electric properties, and the tetragonal phase does not exhibit these properties (Kao, 2004; Carter and Norton, 2007).

In doping, the multiple occupation of ions in the sites A or B in the ABO3 compounds affect the Curie’s temperature and other physical properties (Zhang et al., 2011). The incorporation of isovalent impurities it has no effect on the population of defects; however, the anisovalent impurities (valence different from that of those it replaces) require the formation of opposite charge compensation defects to maintain electrical neutrality. If the replacement cation has a lower valence than the original, electronic holes could free themselves and if the replacement cation has a valence greater than the original cation could release electrons (an electron hole or is the lack of an electron at a position where one could exist in an atom or atomic lattice) (Chan et al., 1986). It is noted that both the valence state and the radius of Er3+ ion (1.00 Å) are intermediate between those of Ba2+ ion (1.42 Å) and Ti4+ ion (0.61 Å). As a result, theoretically Er3+ can occupy either A or B site, depending on Ba/Ti mole ratio (Takada et al., 1987; Dunbar et al., 2004; Mitic et al., 2010; Zhang and Hao, 2013). Then, if Er3+ is added at the BaTiO3 it would have (Chan et al., 1986) Eq. (1):

Based on the above, the structural behavior of BaTiO3 may be affected; this is why this study addresses the effect of the addition of Er3+ on the structural characteristics of BaTiO3. The amount of added erbium will be varied between 0.003 and 0.35 (wt. %) to know the limit of solubility of erbium in BaTiO3. The method used is the solid state reaction, which is an important technique in the preparation of polycrystalline solids. A solid state reaction, also called dry reaction mixture of oxides, is a chemical reaction in which no solvents are used. The advantages of this method (compared to other techniques) are mainly economic and, hence large scale production is frequently based on solid-state reactions of mixed powders (Hernández Lara et al., 2017).


Samples of BaTiO3 doped with Er3+ were elaborated using the solid-state reaction method, by grinding stoichiometric amounts of BaCO3 (Sigma-Aldrich CAS No. 513-77-9 99.0%), TiO2 (Sigma Aldrich CAS No. 1317-80-2 99.99%) and Er2O3 (Sigma-Aldrich CAS Number: 12061-16-4 99.99%) in an agate mortar, with acetone as a control medium according to the equation Ba1-xErxTi1-x/4O3 and x = 0, 0.003, 0.005, 0.01, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35 Er3+ (wt. %). The powders (BaCO3, TiO2 and Er2O3) were previously dried in a muffle-type oven for 24 h at 200 °C before weighting. The mixture was de-carbonated at 900 °C for 12 h using an Al2O3 crucible as a container, and subsequently ground again for 30 min in an agate mortar. The powder mixture obtained was sintered at 1400 °C for 12 h in a platinum crucible in air atmosphere with heating and cooling rates of 5 °C·min-1, using a muffle furnace (Thermolyne model 46200). The powder mixes were ground again for 30 min in an agate mortar and then compacted using uniaxial pressing at 250 MPa in an 8-mm stainless steel die, to produce green pellets of approximately 3 mm thickness. The pellets were sintered at 1400°C for 5 h in air atmosphere with heating and cooling rates of 5 °C·min-1. The structural evolution of the products was evaluated and monitored using X-ray diffraction (diffractometer Equinox 2000 Cu Kα). The analysis of the morphology in the pellets sintered was carried out using a JEOL 6300 SEM. Raman studies for each sample obtained after sintering were performed in a spectrophotometer (Perkin Elmer Spectrum Gx) over the range of 100–1200 wavelength (cm-1). Additionally, to determine contamination of O-H group into the products, IR spectra were recorded for the samples with more significant results in the previous techniques using a Perkin Elmer 2000 FT-IR in the range 700–400 cm–1.


3.1. X-Ray diffractionTOP

The X-ray diffraction patterns of BaTiO3 doped with Er3+ are shown in Fig. 1. A combination of cubic (JCPDS 310174) and tetragonal phases (JCPDS 050626), with the latter being predominant, was obtained. It can be seen from the X-Ray patterns that when Er3+ content was 0.003 ≤ x ≤ 0.35, the presence of a double peak located at 2θ ≈ 46°, indicates the existence of the tetragonal phase (JCPDS 050626) (Hernández Lara et al., 2017), which, as mentioned above, exhibits ferroelectric properties. On the other hand, it can also be noted that when the concentration of Er3+ was x > 0.05, a secondary phase identified as Er2Ti2O7 (JCPDS 731647) was detected in the peaks located at 2θ ≈ 28°, 2θ ≈ 29.6° and 2θ ≈ 35.36° (Fig. 2). It has been reported (Li et al., 2012), that pyrochlores A2B2O7 belong to Fd3m space group, and are a superstructure of the fluorite structure (MO2) but with two cations and one eighth of the oxygen anion absent. Pyrochlores A2B2O7 are important candidates as ceramic waste forms for actinide immobilization and are among the principal host phases currently considered for the disposition of Pu from dismantled nuclear weapons and the ‘‘minor’’ actinides (Yashima et al., 1996; Dobal and Katiyar, 2002). The formation of the secondary phase (Er2Ti2O7) indicates that the solubility limit of Er3+ in the BaTiO3 crystal structure is reached when x = 0.05. Additionally, Fig. 3 shows the sizes of crystallites obtained for each composition estimated from the broadening of the diffraction deflections, by applying the Scherrer equation, (Eq. (2)):

Figure 1.   XRD diffractograms for Ba1-xErxTi1-x/4O3 powders sintered at 1400 °C for 5 h for different values of x.


Figure 2.   XRD diffractograms for Ba1-xErxTi1-x/4O3 powders sintered at 1400 °C for 5 h for different values of x, zoom at 26-36°.


Figure 3.   Sizes of crystallites obtained for powders sintered at 1400 °C for 5 h for different values of x.


Where: t = grain size, λ = wavelength, B = is the line broadening at half the maximum intensity (FWHM), after subtracting the instrumental line broadening, in radians. This quantity is also sometimes denoted as ∆(2θ), q = Bragg angle (in degrees), k = form factor (constant = 1.15).

The estimated average sizes were ~285.9 nm for (110), and 347.6 nm for (111) planes respectively. The absence of trend observed in Fig. 3 can be attributed to the radius of Er3+ ion being intermediate between those of Ba2+ ion and Ti4+ ion. Thereby, the Er3+ could have occupied the A or B site (Zhang et al., 2011).

3.2. Raman spectroscopyTOP

Raman spectroscopy is a spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system. This has the ability to be very sensitive to transitions involving oxygen displacements and can detect the local lattice distortions and crystallographic defects at the molecular level (Yashima et al., 1996; Dobal and Katiyar, 2002). Hence, this technique is appropriate to reveal change from the tetragonal ferroelectric phase to a cubic para-electric phase. Fig. 4 shows the evolution of Raman spectra obtained for powders of BaTiO3 added to different concentrations of Er3+, for 0.003 ≤ x ≤ 0.35 prepared by the solid state reaction. It shows the characteristic depolarized scattering profiles for single and polycrystalline BaTiO3 (Venkateswaran et al., 1998).

Figure 4.   Raman spectra of sintering powders at 1400 °C, 0.003 ≤ x ≤ 0.35.


The plots present the typical BaTiO3 tetragonal phase Raman scattering bands at room temperature at about 250 (A1(TO)), 515 (E(TO) , A1(TO)) and 716 cm-1 (E(LO) , A1(LO)) and a sharp peak at around 305 cm-1(B1, E(TO + LO)) (Asiaie et al., 1996). An extra band was observed about 834 cm-1, and it was noted that this occurs when Er3+ content was Er 0.10≤ x ≤ 0.35. This result can be associated to the formation of the secondary phase (Er2Ti2O7)identified in the Fig. 1 in the peaks located at 2θ ≈ 28°, 2θ ≈ 29.6° and 2θ ≈ 35.36°.

On the other hand, according to the nuclear site group analysis, (Rousseau et al., 1981) Raman active phonons of the tetragonal P4mm (C4v1) crystal symmetry are represented by 3A1+ B1+ 4E. Long-range electrostatic forces induce the splitting of transverse and longitudinal phonons, which results in split Raman active phonons represented by 3[A1(TO)+A1(LO)]+B1+ 4[E(TO)+ E(LO)]. It has been reported (Venkateswaran et al., 1998) that while the cubic phase theoretically does not reveal any Raman active modes, this polymorph generally shows broad bands at around 250 and 520 cm-1, which may be caused by local disorder associated with the position of Ti atoms.

3.3. Infrared spectroscopyTOP

Infrared spectroscopy is the analysis of infrared light interacting with a molecule. It is used to determine functional groups in molecules. IR spectroscopy measures the vibrations of atoms, and based on this, it is possible to determine the functional groups.

Figure 5 shows the IR spectra for Ba1-xErxTi1-x/4O3 powders sintered at 1400 °C for 5 h for x = 0 (BaTiO3), 0.10 and 0.35. From the results, the characteristic absorption bands relating to BaTiO3, which are located at ~545 and ~410 cm–1 (Asiaie et al., 1996), can be clearly seen.

Figure 5.   IR spectra for Ba1-xErxTi1-x/4O3 powders sintered at 1400 °C for 5 h for x = 0 (BaTiO3), 0.10 and 0.35.


No bending vibrations of O-H corresponding to coordinated H2O were observed, which validates the assumption that the synthesis method used generate pure phases of BaTiO3. Garrido-Hernández et al. (2014) reported the presence of OH groups caused by the hydrolysis method used, as well as the presence of CO32– group.

The BaTiO3 is formed of Ti–O6 octahedrons, and the Ba2+ is located at the center of eight Ti–O6 octahedrons. On the other hand, the Ti–O6 octahedron is the most stable form of Ti4+ and is the basic structural element in perovskite BaTiO3.

3.4. Morphology and microstructureTOP

The selected images obtained from SEM-EDS of Er3+ doped BaTiO3 are shown in Fig. 6 for the samples sintered at 1400 °C for 5 h in air atmosphere, with heating and cooling rates of 5 °C·min-1 and x = 0 (a) and x = 0.25 (b). The micrographs consist of rounded grains with a wide grain-size distribution. For the undoped sample (Fig. 5 a), grain sizes average 11 μm and 6 μm for the sample with 0.25 Er3+ (wt. %). This figures shows that grain size diminishes when the concentration of erbium is increased. The SEM images of the sintered pellets shows that Er3+ did not drastically modify the microstructure. Hernández Lara et al. (2017) reported similar sintering structures for Gd3+ doped BaTiO3; this can be attributed to the fact that both of them belonging to the lanthanide group. The incorporation of erbium in the crystalline structure of BaTiO3 was corroborated in the EDS spectra obtained for each of the samples.

Figure 6.   SEM-EDS micrographs of BaTiO3, doped with Er3+: a) x = 0.0, and b) x= 0.25.


The detailed image acquired for the sample of Er3+ doped BaTiO3 with x = 0.005 (Fig. 7) showed higher amounts of inter-granular porosity. In the same way, necks generated in the sintering process of the particles were observed.

Figure 7.   SEM micrograph detail of Er3+ doped BaTiO3, x = 0.005.



Structural evolution of solid solutions of Er3+ doping BaTiO3 (Ba1-xErxTi1-x/4O3) with x = 0, 0.003, 0.005, 0.01, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35 Er3+ (wt. %) was investigated by X-ray diffraction, Raman spectroscopy, Infrared spectroscopy, and scanning electron microscopy. A double deflexion located at 2θ ≈ 46° showed the formation of the tetragonal ferro-electric phase for the patterns in which Er3+ content was 0.003 ≤ x ≤ 0.35.
A secondary phase belonging to Fd3m space group identified as a pyrochlore (Er2Ti2O7) was revealed at the position 2θ ≈ 28°, 2θ ≈ 29.6° and 2θ ≈ 35.36°.
The solubility limit of Er3+ in the crystal structure of BaTiO3 was reached when x = 0.05.
The Raman graphics showed the typical BaTiO3 tetragonal phase scattering bands at around 250 (A1(TO)), 520 (E(TO), A1(TO)) and 720 cm-1 (E(LO), A1(LO)) and a sharp peak at around 306 cm-1(B1, E(TO + LO)). An extra band was observed about 834 cm-1, when Er3+ content was Er 0.10≤ x ≤ 0.35. This result can be associated to the formation of the secondary phase (Er2Ti2O7) identified by X-ray diffraction.
The Infrared spectroscopy patterns indicated the characteristic absorption bands relating to BaTiO3 and no absorption bands contamination of O-H group into the products was observed. The SEM micrographs consisted of rounded grains with a wide grain-size distribution. The EDS analysis confirmed the presence of the Er3+ in the crystalline structure of BaTiO3.


The author is grateful to PRODEP and CONACyT-México for the financial support.



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