RE Dopants Research Articles

Humidity-resistant hydrogen sensors based on rare-earth-doped tin dioxide nanofibers with hydrophobic mesoporous silica sieve encapsulation

Air humidity is a major factor that degrades the performance and long-term stability of metal-oxide-semiconductor (MOS) based gas sensors. In this work, we propose an encapsulation strategy by coating a mesoporous silica molecular sieve (SBA-15) on rare earth doped tin oxide (RE-SnO2) nanofibers for humidity-resistant hydrogen detection. In this design, the hydrophobic SBA-15 sieve layer effectively blocks the water molecules without affecting hydrogen diffusion, while the RE dopant greatly improves the responsivity and lowers down the operating temperature of the sensors, As a result, the Er-SnO2/SBA-15 and Tb-SnO2/SBA-15 sensors respectively show the maximum response values of 27.71 and 33.68 (to 10 ppm hydrogen at 280 °C, 4.67 and 5.67 times that of the bare SnO2 ones, respectively), short response/recovery time (< 1.0 s / < 1.0 s), as well as a low limit of detection for hydrogen (200 ppb) and a good gas selectivity. Under the protection of the SBA-15 sieve layer, the response retention of the sensors is significantly improved when the humidity increases from 25% to 85% RH (Er-doping, from 38.8% to 60.0%; Tb-doping, form 25.6–57.8%). Besides, further analysis on enhancement mechanism of response indicates that the SBA-15 coating contribute about 1/3 of the response enhancements via its own hydrogen physical adsorption capacity and the induced oxygen vacancies during the calcination processes.

Enhancing humidity sensitivity properties through RE (Er, La, and Sm) dopants in TiO2 nanofiber composites

Enhancing humidity sensitivity properties through RE (Er, La, and Sm) dopants in TiO2 nanofiber composites

Role of 4f electrons and 3d-4f hybridization in metal-insulator transition in RE (La, Nd, Sm, Eu, Dy and Er)-doped vanadium dioxide for thermochromic applications

Vanadium dioxide is a promising thermochromic material for novel applications to smart optoelectronic devices due to its reversible insulator-to-metal transition which is accompanied by rapid variation in its optical properties. In this work, rare-earth (La, Nd, Sm, Eu, Dy and Er) dopants substituting vanadium site were investigated in detail to control the phase transition temperature (TMIT) and optical properties of VO2. It is found that TMIT is mainly related to the nature of 3d-4f hybridization in RE-doped VO2(M1): the direct overlapping of 3d-4f orbitals contributes to V–V dimerization, but it is less pronounced to lower TMIT; the indirect 3d-4f interaction via O-2p makes 4f electrons itinerant to egπ states to assist MIT from M1 to R phase at lower temperatures. The dominating nature of 3d-4f hybridization varies with changing RE dopant's ionic radius and electronegativity. Er offered the lowest TMIT with a decreasing rate of 12.8 °C/at. % due to effective 4f-O2p-3d hybridization. RE dopants were also found effective in changing optical properties by scaling Eg1 and Eg2 bandgaps of VO2. Hence, the fashion of 3d-4f interaction in RE-doped VO2 is found to play important role in modulating thermochromic properties of VO2 for smart window applications and smart optoelectronics devices.

Luminescence characteristics and kinetic parameters of LiBaPO4: Tb3+, Dy3+ phosphors synthesized by sol-gel method

LiBaPO4: Tb3+, Dy3+ phosphors were prepared via sol-gel method by using the stoichiometric amounts of lithium nitrate LiNO3, barium nitrate Ba(NO3)2 and ammonium dihydrogen phosphate NH4H2PO4 as base materials. Morphology by scanning electron microscopy (SEM), structure by X-ray diffraction (XRD), thermal properties by Differential thermal analysis (DTA)/Thermogravimetric Analysis (TGA) and structural characteristics by Fourier transform infrared spectroscopy (FT-IR) were investigated. This paper presents luminescence properties using spectra from radioluminescence (RL), photoluminescence (PL), cathodoluminescence (CL) and, thermoluminescence (TL) and the influence of RE dopants (Tb3+, Dy3+) on the luminescent behavior of LiBaPO4. Computerized Glow Curve Deconvolution (CGCD) and Peak Shape Method were used to determine the kinetic parameters and the obtained results were evaluated. The RL results of un-doped LiBaPO4 showed the presence of a well-defined peak at 417 nm and a weaker band around 685 nm. Strong emissions were detected in the sample doped with Dy3+ correspond to 4F9/2→6Hj transitions. Blue, yellow and red emissions were observed with transitions of 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 and 4F9/2 → 6H11/2, respectively. As for LiBaPO4: Tb3+, green emissions originated from the characteristic transitions (5D3 → 7FJ (j = 6–3) and 5D4 → 7FJ (j = 6–1)) of Tb+3 ion was seen. The RL, PL and CL spectra were identical, suggesting these green emissions. Dy3+ doped sample has three glow curves located at 72 °C, 145 °C and 204 °C, while the main temperature peak is measured at 240 °C for Tb3+ doped sample. Chromotographic studies of LiBa0·98PO4: Dy3+0.02 reveals that calculated x and y color coordinates (0.3122, 0.3233) are very close to the white light.

Doping rare earth cations with an additional chemical reduction synergistically weakened the photocatalytic performance of ceria.

Chemical reducing or rare earth cations (RE) doping was normally employed to promote the photocatalytic performance of ceria, aimed to evaluate their cooperation influences, ceria was obtained by decomposing homogenously RE (RE = La, Sm, and Y)-doped CeCO3OH in H2. XPS and EPR results evidenced that the excess oxygen vacancies (OVs) were formed in RE-doped CeO2 compared to the un-doped ceria. However, all the RE-doped ceria unexpectedly showed an impeded photocatalytic activity towards to methylene blue (MB) photodegradation. The 5% Sm-doped ceria had the best MB photodegradation ratio of 81.47% after 2-h reaction in all RE-doped samples, which was lower than that of 87.24% for the un-doped ceria. After doping RE cations and chemical reducing, the band gap of ceria were almost narrowed, while the PL spectra and photo-electro characterizations indicated that the separation efficiency of photo-excited e-/h+ (electrons/holes) was reduced. The RE dopants and formed excess OVs including inner and surface OVs was proposed to promote the recombination of e-/h+ which further hindered the generation of active species of ·O2- and ·OH, and finally weakened the photocatalytic activity of ceria.

Influence of RE (Pr3+, Er3+, Nd3+) doping on structural, vibrational and enhanced persistent photocatalytic properties of ZnO nanostructures

Rare earth (RE- Pr, Er and Nd) doped ZnO nanostructures were prepared through simple wet chemical precipitation route. The RE doping induced interesting morphological transition from spherical to flower like structures were analyzed. The X-ray diffraction (XRD) measurements revealed that the prepared materials were of highly crystalline in nature and RE dopant ions did not altered the crystal structure of ZnO. The microstrain of ZnO was altered with respect to the nature of dopants. In the case of the Pr doped ZnO, X-ray photoelectron spectroscopy (XPS) analysis confirmed that the dopant (Pr) ions successfully substituted in the ZnO lattice. Raman spectra revealed RE doping induced lower energy side shift and variation in intensity of the peaks related to the characteristic phonon modes of ZnO. In the case of Nd doped ZnO nanostructures, dopant induced suppression in classical Raman modes and evolution of multiphonon related modes were identified. Optical diffuse reflectance spectral (DRS) measurements, along with the characteristic excitonic band of ZnO, other bands associated to the transitions of 4f energy levels related to the RE ions were observed. The partially filled 4f orbitals led to the enhanced photocatalytic activity in RE doped ZnO nanostructures. The observed enhanced photocatalytic activity in RE doped ZnO when compared to bare ZnO was discussed. The decolorization efficiency of MB ensued the following order 96 > 94 > 86 > 78% for ZnErO, ZnNdO, ZnPrO and ZnO, respectively.

Radiation Induced Defects and Thermoluminescence Characteristics in Eu, Dy and Eu/Dy Doped-Quartz Sol-Gel by 2 Gy Beta and 2 MeV ⁴He⁺ Irradiations

Thermoluminescence (TL) of pure and Eu3+ and Dy3+ doped synthesis quartz was synthesized and their ion beam and thermoluminescence properties were investigated. The as prepared, doped and co-doped quartz and the effects of imparting 2 Gy beta dose and 2MeV 4He+ ion beam irradiation is investigated. The basic model proposed and can explain our observations is that, the dominant signals from the as prepared material arise from the incorporation of the transitions within the RE dopants enhanced by the intensity from the intrinsic or host defect sites within the synthesis quartz network. The complex shape TL glow curves indicate that irradiation causes major distortions to the lattice with the incorporation of extrinsic impurities and RE doping processes, induce perturbations and alter the energy levels pattern of the free ions and assigned transitions probabilities in a manner that that depends on the dopants, their concentrations and the host material. The larger Eu ions stabilize the emission more than that of the Dy ions. The TL peak temperatures are commonly correlated via charge transfer processes and scale with the ions size, in such a manner that the close proximity (or shallow traps) allows lower temperature electron release, whereas the more distant variants (deep traps) are less distorted, but are still able to couple to the higher energy orbitals of the Eu ions.

Ionic size dependence of distribution coefficient for rare-earth dopants in YVO4 crystal

This paper reports a systematic study of distribution coefficient in YVO4 for the entire series of trivalent rare-earth dopants (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc). For this aim, single crystals for each RE dopant were flux-grown under a fixed condition, with the starting ratio of Y0.9RE0.1. The compositions of the grown crystals were then determined using inductively coupled plasma emission spectroscopy. The distribution coefficient is close to 1 when the size mismatch between the dopant ion and the host Y3+ ion is within about ±3%, and drops off in a similar manner for both larger and smaller dopants. The distribution coefficients for the largest (La3+) and smallest (Sc3+) dopants are 0.2 and 0.07, respectively.

Influence of rare earth addition in cobalt ferrite thin films obtained by pulsed laser deposition

The influence of rare earth (RE = Dy, Gd, Yb) ion doping on the structural, magnetic and optical properties of cobalt ferrite thin films was studied. CoFe2-xRExO4 (x = 0.01; 0.03; 0.05; 0.1; 0.2; 0.3) films were obtained by pulsed laser deposition on silicon substrates. The X-ray diffraction and Raman spectroscopy results on the bulk materials, which were used as targets during deposition, revealed the formation of residual phases as the concentration of RE dopant was increased. However, the annealed thin films presented diffraction lines and vibrational modes corresponding only to cobalt ferrite. A lower crystallinity of the deposited samples was observed when higher RE concentrations were used. Due to the substitution of Fe by RE elements which possess large ionic radii, the lattice parameter of the thin films presented a monotonous increase. The magnetic response of the nanostructures was correlated to the magnetic moment of the RE dopant and to the structural properties of the films. The optical bandgaps derived from the reflectance spectra presented an increasing trend as the Yb and Dy concentrations were augmented.

Theoretical study of the electronic and optical properties of rare-earth (RE = La, Ce, Pr, Nd, Eu, Gd, Tb)-doped VO2 nanoparticles

Vanadium dioxide (VO2) is an important thermochromic material due to its reversible metal-insulator transition at 340 K. However, the high phase transition temperature of VO2 prevents its practical application in smart windows. Here, we use first-principles calculations to study the effect of rare-earth (RE = La, Ce, Pr, Nd, Eu, Gd, Tb) dopants on the variation of the local octahedral volumes, lattice distortion of VO2 and dimerization of the V-V chain in VO2. Interestingly, Tb and La dopants with a concentration of 3.1 at.% decreased the phase transition temperature of VO2 to 206 K and 225 K, respectively. Moreover, three factors, including the V-V chain change, distortion of the REO6 octahedron, and formation of impurity states contributed by RE-f states, assist the phase transition of VO2. Additionally, the incorporation of an RE dopant scaled the band gap of VO2 and further tuned its near-IR absorption. These findings provide novel insights and guidance on chemically tailoring the phase transition of VO2.

Structural Distortion, Spin-Phonon Coupling, Interband Electronic Transition, and Enhanced Magnetization in Rare-Earth-Substituted Bismuth Ferrite.

Rare-earth ions (RE = La3+, Nd3+, and Er3+) substituted BiFeO3 (BFO) ceramics were synthesized by a conventional solid-state sintering procedure. X-ray diffraction patterns and Raman spectra confirm a rhombohedral R3c symmetry in all samples with significant distortion in FeO6 octahedron, as well as the occurrence of remarkable spin-phonon coupling and notable change in magnetic transition temperature induced by RE dopants. The enhanced magnetization was observed in all RE-doped BFO ceramics, unveiling that the spatial spin structure of BFO should be perturbed by RE dopants. Diffuse reflectance spectra show a conspicuous evolution of interband electronic transitions in RE-doped BFO ceramics. Especially, the two crystal-field d-d band transitions (6A1g→4T1 and 6A1g→4T2g) exhibit a linear red-shift behavior with the reduction in the cell volume, which is well-linked with a linear tendency of increased magnetization. On the basis of these investigations, a possible mechanism was proposed in this paper to demonstrate the correlation between the structural distortion, interband electronic transitions, and magnetic properties in RE-doped BFO ceramics.

Mid-temperature deep removal of hydrogen sulfide on rare earth (RE = Ce, La, Sm, Gd) doped ZnO supported on KIT-6: Effect of RE dopants and interaction between active phase and support matrix

Rare earth oxides (RE=Ce, La, Sm and Gd) doped ZnO supported on KIT-6 sorbents (RE-ZnO/KIT-6) were synthesized by sol-gel method and their performance for deep removal of H2S (bellow 0.1 ppmv) from gas stream at medium temperature was tested. The RE dopants (except Ce) significantly enhance the deep desulfurization capacity of ZnO/KIT-6 sorbent and maintained higher sulfur uptake capacities upon multiple cycles of regeneration by a simple thermal oxidation in 10v% of O2 in N2 atmosphere. The results of SAXS, XRD, N2 physisorption, TEM, FIIR, and XPS implied that the KIT-6 structure of loading metal oxides remained intact. It was found that RE could hinder the ZnO crystal ripening during calcination resulted in smaller ZnO particles, enhance the interaction of ZnO and silica matrix to improve the dispersion of active phase on KIT-6. Furthermore, by increasing the outlayer electron density of Zn atom and oxygen transfer ability, the synergistic effect considered to be favorable for RE-ZnO/KIT-6 sulfidation. Even though the performance of improving ZnO dispersion was weaker than that of Sm and Gd, La-ZnO/KIT-6 performs the best deep desulfurizers by changing the surface chemical atmosphere for ZnO. Steam in the gas stream inhibited the capture of H2S by ZnO in the sorbents, in the case of La-ZnO/KIT-6, the steam content should control as lower as 5v% to ensure the desulfurization efficiency and precision.

Influence of rare earth (RE=Nd, Y, Pr and Er) doping on the microstructural and optical properties of ceria nanostructures

Nanopowders of Ce0.9RE0.1O1.95 (RE=Nd, Y, Pr and Er) were synthesized by nitrate-fuel combustion method and calcinated at 700°C for 2h to obtain completely crystalline structures. The effect of RE dopants on the crystalline nature, lattice parameters, and microstructural parameters such as microstrain, stress, and deformation energy density of ceria was evaluated through uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM) by using the X-ray diffraction (XRD) data. The results revealed that the microstructural parameters were considerably altered with respect to the dopants. The transmission electron microscope (TEM) graphs and their corresponding selected area diffraction (SAED) patterns of ceria nanoparticles confirmed that all doped ceria powders are crystalline with the wide range of particle size distributions aligned in all the directions. The optical diffuse reflectance spectroscopy (DRS) measurements showed a band at around 340nm attributed to the transitions of charge-transfer between O 2p and Ce 4f orbitals in cerium oxide and RE doped CeO2 exhibited the reflectance band in the visible regions due to the transition of 4f energy levels of RE ions. Photoluminescence (PL) spectra of RE doped ceria showed the blue-green emission bands.

Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films.

The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.

Luminescence spectroscopy of Ln-doped Bi-containing phosphates and molybdates

The photoluminescence (PL) emission and excitation spectra of undoped and doped with rare-earth (RE = Eu, Tb) ions K3Bi5(PO4)6 and K2Bi(PO4)(MoO4) crystals are studied in 3.7–14 eV region of the excitation photon energies at T = 8 and 300 K. The mechanisms of the host-related and RE-related luminescence in 3.7–7 eV region of the excitation photon energies are revealed in comparative analysis of the PL spectra of studied compounds. It is assumed that the excitation mechanisms of host luminescence of K3Bi5(PO4)6 and K2Bi(PO4) (MoO4) crystals below 4.8 eV are related to Bi3+ ions in oxygen surrounding. An efficient energy transfer from the Bi3+-related luminescence centers to the emitting RE centers exists in crystals with low concentration of the RE dopants (1%). The PL excitation spectra of K3Bi5(PO4)6 crystals with high concentration of Eu dopants are formed by O – Eu CT transitions.

Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications.

The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.

Rare Earth-Doped BiFeO3Thin Films: Relationship between Structural and Magnetic Properties

Rare Earth- (RE-) doped BiFeO3(BFO) thin films were grown on LaAlO3substrates by using pulsed laser deposition technique. All of BFO films doped with 10% of RE show a single phase of rhombohedral structure. The saturated magnetization in the Ho- and Sm-doped films is much larger than those reported in literature and was observed at a quite low field as of 0.2 T. As for Pr- and Nd-doped BFO films, Fe2+amount is not dominant; thus, ferromagnetism is not favored. As the RE concentration goes up to 20%, all compounds have drastically gone through a structural transition. The RE-doped BFO films have changed from rhombohedral to either pure orthorhombic phase (for Ho, Sm), or a mixed phase of orthorhombic and tetragonal (for Pr, Nd), or pure tetragonal (for Eu). We observed magnetic properties of RE-doped BFO films have significantly changed. While 20% Ho/Sm-doped BFO films have ferromagnetism degraded in comparison with the 10% doping case, the 20% Pr/Nd-doped BFO thin films, whose structure is a mixed phase, have magnetic ordering improved due to the fact that the Fe2+amount has become greater. It seems that one can control the magnetic properties of BFO films by using appropriate RE dopants and concentrations.

Magnetic scattering and electron pair breaking by rare-earth-ion substitution in BaFe2As2 epitaxial films

The effect of electron doping by trivalent charge state rare-earth-ion (RE = La, Ce, Pr and Nd) substitutions on the superconductivity in BaFe2As2 was examined using epitaxial films. Each of the RE substitutions suppressed the resistivity anomaly associated with magnetic/structural phase transitions, leading to resistivity drops and superconductivity transitions. Bulk superconductivity was observed at the maximum onset critical temperature (Tconset) of 22.4 K for La doping and 13.4 K for Ce doping, while only broad resistivity drops were observed at 6.2 K for Pr doping and 5.8 K for Nd doping although zero resistivity and the distinct Meissner effect were not observed at least down to 2 K. The decrease in Tconset with increasing the number of RE 4f electrons cannot be explained in terms of the crystalline quality or crystallographic structure parameters of BaFe2As2 films. It was clarified, based on resistivity–temperature analyses, that magnetic scattering became increasingly significant in the above order of RE dopants. The negative magnetoresistance was enhanced by Ce and Pr doping, implying that the decrease in Tc originates from magnetic pair breaking by interaction of the localized 4f orbitals in the RE dopants with the itinerant Fe 3d orbitals.

${\rm MgB}_{2}$ Doping by Rare-Earth Metals and Borides

This study refers to Rare-Earth elements ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm RE}={\rm Ce}$</tex></formula> , Sm, Gd) doping of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MgB}_{2}$</tex></formula> bulk materials. The synthesis of doped <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MgB}_{2}$</tex></formula> has been performed by Reactive Liquid Mg Infiltration process (Mg-RLI): the RE additives, in the form either of pure metallic powder or of borides powder, have been mixed with the starting boron powder. The RE dopants could operate through two different doping mechanisms: the substitution of Mg ions in the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MgB}_{2}$</tex></formula> crystal lattice or the growth of intergrain boride phases of nanometric size that modify the grain boundaries of the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MgB}_{2}$</tex></formula> polycrystals. The structure of the resulting RE-doped <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MgB}_{2}$</tex></formula> has been characterized by X-ray diffraction and SEM/EDS analysis. The effects of this kind of doping on the high magnetic field properties of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MgB}_{2}$</tex></formula> have been measured by magnetization loops.

Composition and temperature-induced structural evolution in La, Sm, and Dy substituted BiFeO3 epitaxial thin films at morphotropic phase boundaries

Detailed structural investigations on the substitution-induced structural phase transition from the rhombohedral phase to an orthorhombic phase in (Bi,RE)FeO3 epitaxial thin films (RE = La, Sm, and Dy) grown on (100) SrTiO3 substrates are presented. X ray diffraction reveals that the unit cell dimensions of the orthorhombic phase are strongly dependent on the type of the RE dopant. For RE = La3+ ion, which has an ionic size comparable to the Bi3+ ion, the unit cell is found to be a0 × a0 × 2a0, where a0 is the pseudo-cubic lattice parameter. This is in contrast with the √2a0 × √2a0 × 2a0 unit cell for the case of smaller ionic radius RE (= Sm and Dy) elements. While clear double-hysteresis loops in the polarization versus electric-field curves due to field-induced transitions are observed for smaller ionic radius RE (= Sm and Dy), no signature of the double hysteresis loops is observed for the RE = La case across the structural boundary. We have also performed systematic tracking of the structural phases as functions of the RE composition and temperature, based on which we propose a phase diagram. This work reveals that the ionic size of the RE element plays a critical role in the evolution of the structural and functional properties of RE-substituted BiFeO3 thin film materials systems.