Annealing effects on the structural and dielectric properties of (Nb + In) co-doped rutile TiO2 ceramics

Density functional theory calculations were conducted to investigate the electronic structures of rutile Ti₁₆O₃₂, Ti₁₃Nb₂InO₃₂, and Ti₁₃Nb₂InO₃₁ systems. High density (Nb + In) co-doped rutile TiO₂ ceramics were successfully prepared by one modified solid state method. XRD, XPS, Raman scattering and FT-IR measurements were performed to investigate the structural properties of the (Nb + In) co-doped rutile TiO₂ ceramics annealed in different atmospheres. The lattice parameters for the (Nb + In) co-doped rutile TiO₂ ceramics were enlarged slightly after they were annealed in air and oxygen. Raman scattering results indicate that the E_g modes are quite sensitive to oxygen vacancy in comparison with the other Raman active modes. The ceramics annealed in oxygen at 873 K exhibit the best dielectric performance with giant dielectric permittivity (>14 000) and small dielectric loss (<0.2) over the frequency range from 40 Hz to 1 MHz.

Density functional theory calculations were conducted to investigate the electronic structures of rutile Ti₁₆O₃₂, Ti₁₃Nb₂InO₃₂, and Ti₁₃Nb₂InO₃₁ systems.     

Fe3+/Nb5+ Co-doped rutile–TiO2 nanocrystalline powders prepared by a combustion process: preparation and characterization and their giant dielectric response

Fe³⁺/Nb⁵⁺ co-doped TiO₂ (FeNb-TO) nanocrystalline powders were prepared by a combustion process. A pure rutile–TiO₂ phase of powders and sintered ceramics with a dense microstructure was achieved. Both co-dopants were homogeneously dispersed in the ceramic microstructure. The presence of oxygen vacancies was confirmed by Raman and X-ray photoelectron spectroscopy techniques. The low-frequency dielectric permittivity enhanced as co-doping concentration increased. The thermally activated giant-dielectric relaxation of FeNb-TO ceramics was observed. Removing the outer-surface layer had a slight effect on the dielectric properties of FeNb-TO ceramics. Density functional theory (DFT) calculation showed that, in the energy preferable configuration, the 2Fe atoms are located near the oxygen vacancy, forming a triangle-shaped FeV_oTi defect complex. This defect cluster was far away from the diamond-shaped 2Nb2Ti defect complex. Thus, the electron-pinned defect-dipoles (EPDD) cannot be formed. The giant-dielectric relaxation process of the FeNb-TO ceramics might be attributed to the interfacial polarization associated with electron hopping between Ti³⁺/Ti⁴⁺ ions inside the grains, rather than due to the surface barrier layer capacitor (SBLC) or EPDD effect.

Fe³⁺/Nb⁵⁺ co-doped TiO₂ (FeNb-TO) nanocrystalline powders were prepared by a combustion process.     

Enhanced dielectric properties with a significantly reduced loss tangent in (Mg2+, Al3+) co-doped CaCu3Ti4O12 ceramics: DFT and experimental investigations

CaCu₃Ti₄O₁₂ and CaCu_2.95Mg_0.05Ti_3.95Al_0.05O₁₂ ceramics were fabricated via a solid-state reaction method. A single-phase of CaCu₃Ti₄O₁₂ was found in these two ceramics. Very great grain size expansion was produced by co-doping with Mg²⁺ and Al³⁺. DFT results indicate that both Mg and Al atoms preferentially occupy Cu sites, creating liquid-phase sintering decomposition at grain boundary layers. Very high dielectric permittivity of ∼58 397 and low loss tangent of about 0.047 were achieved in a CaCu_2.95Mg_0.05Ti_3.95Al_0.05O₁₂ ceramic. Additionally, the temperature stability of the dielectric response was improved. Better dielectric properties in the co-doped ceramic have possible origins from enhanced grain boundary responses, especially from the influences of metastable phases and oxygen enrichment at the grain boundaries. Experimental and computational results indicate that the colossal dielectric properties in CaCu₃Ti₄O₁₂ ceramics might be correlated with an internal barrier layer capacitor structure.

Mg and Al atoms preferentially occupy Cu sites, creating liquid-phase sintering decomposition at grain boundary layers. This results in very high dielectric permittivity and a low loss tangent of the CaCu_2.95Mg_0.05Ti_3.95Al_0.05O₁₂ ceramic.     

Multifunctional Nd3+ substituted Na0.5Bi0.5TiO3 as lead-free ceramics with enhanced luminescence,ferroelectric and energy harvesting properties

Herein, we present comprehensive investigations of the optical and electrical properties of Nd³⁺ substitution in sodium bismuth titanate ceramics (NBNT) with varying Nd³⁺ concentration. The room temperature photoluminescence (PL) emission for both unpoled and poled samples is observed to be a maximum for an Nd³⁺ substitution of 1 mol%. Upon poling, the PL intensity is observed to be quenched, consistent with the obtained XRD data, indicating an electric-field induced structural ordering towards higher symmetry, confirmed with the help of structural refinement. The evaluated ferroelectric to relaxor and antiferroelectric relaxor T_(F–R) was observed clearly from the poled dielectric–loss curve for the 1 mol% of Nd³⁺ substitution. Furthermore, the optimized NBNT exhibited a lower E_c and a higher off-resonance figure of merit (FOM_off) for energy harvesting by 12% and 30%, respectively, in comparison with un-doped NBT.

Herein, we present investigations on the effect of electrical poling on the optical and electrical properties of Nd³⁺ substituted NBT ceramics with varying Nd³⁺ concentrations.     

A new approach to improve the electrochemical performance of ZnMn2O4 through a charge compensation mechanism using the substitution of Al3+ for Zn2+

ZnMn₂O₄ and Zn_1−xAl_xMn₂O₄ were synthesized by a spray drying process followed by an annealing treatment. Their structural and electrochemical characteristics were investigated by SEM, XRD, XPS, charge–discharge tests and EIS. XPS data indicate that the substitution of Al³⁺ for Zn²⁺ causes manganese to be in a mixed valence state by a charge compensation mechanism. Moreover, the presence of this charge compensation significantly improves the electrochemical performance of Zn_1−xAl_xMn₂O₄, such as increasing the initial coulombic efficiency, stabilizing the cycleability as well as improving the rate capability. The sample with 2% Al doping shows the best performance, with a first cycle coulombic efficiency of 69.6% and a reversible capacity of 597.7 mA h g⁻¹ after 100 cycles. Even at the high current density of 1600 mA g⁻¹, it still retained a capacity of 558 mA h g⁻¹.

This work reports the nonequivalent substitution of ZnMn₂O₄. This is a new approach to improve the electrochemical performance of ZnMn₂O₄ through a charge compensation mechanism using the substitution of Al³⁺ for Zn²⁺.     

Constructing Rh–Rh3+ modified Ta2O5@TaON@Ta3N5 with special double n–n mutant heterojunctions for enhanced photocatalytic H2-evolution

A multiple core–shell heterostructure Rh–Rh³⁺ modified Ta₂O₅@TaON@Ta₃N₅ nanophotocatalyst was successfully constructed through nitriding Rh³⁺-doped Ta₂O₅ nanoparticles, which exhibited a much higher carrier separation efficiency about one order of magnitude higher than the Ta₂O₅@Ta₃N₅ precursor, and thus an excellent visible light photocatalytic H₂-evolution activity (83.64 μmol g⁻¹ h⁻¹), much superior to that of Rh anchored Ta₂O₅@TaON (39.41 μmol g⁻¹ h⁻¹), and improved stability due to the residual Rh–O/N in the Ta₃N₅ shell layer. Rh-modifying significantly extended light absorption to the overall visible region. Localized built-in electric fields with hierarchical potential gradients at the multiple interfaces including a Rh/Ta₃N₅ Schottky junction and double n–n Ta₃N₅/TaON/Ta₂O₅ mutant heterojunctions, drove charge carriers to directionally transfer from inside to outside, and efficiently separate. Enhanced photoactivity was ascribed to a synergetic effect of improved light absorption ability, increased carrier separation efficiency, and accelerated surface reaction. A promising strategy of developing excellent Ta₃N₅-based photocatalysts for solar energy conversion is provided by constructing double n–n mutant heterojunctions.

Localized built-in electric fields at multiple hierarchical interfaces facilitate the efficient separation and fast inside-out directional transfer of photogenerated carriers.     

Optical and structural properties of the Fe3+-doped Lu3Al5O12:Ce3+ garnet phosphor

A novel series of Lu₃Al_5−xFe_xO₁₂:Ce³⁺ (0.00 ≤ x ≤ 0.45) garnets were obtained by the solid-state reaction method at 1200 °C. The obtained materials were characterized by X-ray diffraction, Rietveld refinement, UV-Vis diffuse reflectance spectroscopy, absorption spectroscopy, and photoluminescence spectroscopy. Fe³⁺ doping allowed obtaining pure-phase materials at temperatures and times below those reported up to now. On the other hand, the materials reached an improved blue absorption and a tunable emission from green to orange. These optical properties are attributable to a red-shift phenomenon due to an increase of the crystal field splitting in the Ce³⁺ energy-levels. Moreover, the obtained phosphors exhibited a high quantum yield (55–67%), excellent thermal photoluminescence stability (up to 200 °C), and high color conversion, making the obtained phosphors promising candidates for w-LEDs.

A novel series of Lu₃Al_5−xFe_xO₁₂:Ce³⁺ (0.00 ≤ x ≤ 0.45) garnets were obtained by the solid-state reaction method at 1200 °C.     

TiO2/Fe2O3 heterostructures with enhanced photocatalytic reduction of Cr(vi) under visible light irradiation

We report a study on the synthesis of TiO₂/Fe₂O₃ (TF) nanocomposites and their photocatalytic performance under visible-light irradiation. The characterization of structure and morphology shows that hematite Fe₂O₃ was deposited on anatase TiO₂ nanoparticles with particle sizes in the range of 20–100 nm. In contrast to pure TiO₂ and pure Fe₂O₃, the nanocomposites exhibited remarkable photocatalytic activity. For example, the photoreduction efficiency of TF0.5 reaches 100% for a 100 ppm Cr(vi) solution within 160 minutes. The photochemical properties were studied by various methods. Finally, we conclude that the excellent performance of the photocatalysts is mainly attributed to two aspects: the enhanced absorption of visible light and the synergistic effect of an internal electric field at the heterojunction and citric acid for promoting the separation of electron–hole pairs.

A TiO₂/Fe₂O₃ heterojunction with an internal electric field was constructed for enhancing photocatalytic reduction efficiency of Cr(vi).     

Effect of Bi2O3 content on the microstructure and electrical properties of SrBi2Nb2O9 piezoelectric ceramics

Lead-free ceramics, SrBi₂Nb₂O₉–xBi₂O₃ (SBN–xBi), with different Bi contents of which the molar ratio, n(Sr) : n(Bi) : n(Nb), is 1 : 2(1 + x/2) : 2 (x = −0.05, 0.0, 0.05, 0.10), were prepared by conventional solid-state reaction method. The effect of excess bismuth on the crystal structure, microstructure and electrical properties of the ceramics were investigated. A layered perovskite structure without any detectable secondary phase and plate-like morphologies of the grains were clearly observed in all samples. The value of the activation energy suggested that the defects in samples could be related to oxygen vacancies. Excellent electrical properties (e.g., d₃₃ = 18 pC N⁻¹, 2P_r = 17.8 μC cm⁻², ρ_rd = 96.4% and T_c = 420 °C) were simultaneously obtained in the ceramic where x = 0.05. Thermal annealing studies indicated the SBN–xBi ceramics system possessed stable piezoelectric properties, demonstrating that the samples could be promising candidates for high-temperature applications.

Lead-free ceramics, SrBi₂Nb₂O₉–xBi₂O₃ (SBN–xBi), with different Bi contents of which the molar ratio, n(Sr) : n(Bi) : n(Nb), is 1 : 2(1 + x/2) : 2 (x = −0.05, 0.0, 0.05, 0.10), were prepared by conventional solid-state reaction method.     

Ultrasonic spray pyrolysis synthesis of TiO2/Al2O3 microspheres with enhanced removal efficiency towards toxic industrial dyes

Developing low-cost and highly effective adsorbent materials to decolorate wastewater is still challenging in the industry. In this study, TiO₂-modified Al₂O₃ microspheres with different TiO₂ contents were produced by spray pyrolysis, which is rapid and easy to scale up. Results reveal that the modification of γ-Al₂O₃ with TiO₂ reduced the crystallite size of Al₂O₃ and generated more active sites in the composite sample. The as-synthesized Al₂O₃–TiO₂ microspheres were applied to remove anionic methyl orange (MO) and cationic rhodamine B (RB) dyes in an aqueous solution using batch and continuous flow column sorption processes. Results show that the Al₂O₃ microspheres modified with 15 wt% of TiO₂ exhibited the maximum adsorbing capacity of ∼41.15 mg g⁻¹ and ∼32.28 mg g⁻¹ for MO and RB, respectively, exceeding the bare γ-Al₂O₃ and TiO₂. The impact of environmental complexities on the material''s reactivity for the organic pollutants was further delineated by adjusting the pH and adding coexisting ions. At pH ∼5.5, the TiO₂/Al₂O₃ microspheres showed higher sorption selectivity towards MO. In the continuous flow column removal, the TiO₂/Al₂O₃ microspheres achieved sorption capacities of ∼31 mg g⁻¹ and ∼19 mg g⁻¹ until the breakthrough point for MO and RB, respectively. The findings reveal that TiO₂-modified Al₂O₃ microspheres were rapidly prepared by spray pyrolysis, and they effectively treated organic dyes in water in batch and continuous flow removal processes.

Developing low-cost and highly effective adsorbent materials to decolorate wastewater is still challenging in the industry.     

Fabrication of La3+ doped Ba1−xLaxTiO3 ceramics with improved dielectric and ferroelectric properties using a composite-hydroxide-mediated method

Lanthanum (La³⁺) doped Ba_1−xLa_xTiO₃ (x = 0.0, 0.0025, 0.005, 0.0075) ceramics were synthesized by the composite-hydroxide-mediated method. Rietveld refinement of the XRD patterns confirmed the formation of a perovskite crystal structure that transforms from tetragonal to pseudo-cubic with La³⁺ doping content (x). Scanning electron microscopy displayed a dense and homogeneous microstructure with reduced grain size on La³⁺ doping. The frequency and temperature-dependent dielectric measurements showed an improvement in the dielectric permittivity, a decrease in the ferroelectric–paraelectric transition temperature, and an increase in the dielectric diffusivity with increasing La³⁺ doping content. Complex impedance analysis indicated the semiconducting behavior with a positive temperature coefficient of resistance effect, which could be explained in terms of a charge compensation mechanism in the donor doped BaTiO₃. The ferroelectric hysteresis loops revealed that these ceramics are ferroelectric in nature, while an improvement in the energy storage density and energy storage efficiency was observed for the doped samples due to reduced grain size on La³⁺ doping. Here, the sample with x = 0.005 has a high dielectric permittivity, a low dielectric tangent loss, and the highest energy storage efficiency. This makes this composition interesting for energy storage applications.

The improved dielectric and energy storage properties of La³⁺-doped BaTiO₃ ceramics make them attractive for use in energy storage applications.     

An upconversion luminescence and temperature sensor based on Yb3+/Er3+ co-doped GdSr2AlO5

GdSr₂AlO₅:Yb³⁺/Er³⁺ micro-particles were synthesized by a simple solid state method. The structure, morphology, size and upconversion luminescence features have been characterized. These results indicated that GdSr₂AlO₅ has a contracted tetragonal cell and has irregular block shaped particles with sizes of about 5 μm. During upconversion, green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) (527 nm, 549 nm) and red (⁴F_9/2 → ⁴I_15/2) (665 nm) emissions had been observed, both of which occurred via a two-photon population process. In addition, green UC emission characteristics were studied, and it was found that its temperature ranged from 293 K to 473 K and the sensitivity was 0.0054 K⁻¹ at 473 K. This indicated that GdSr₂AlO₅:Yb³⁺/Er³⁺ micro-particles may have potential application in high temperature environments for safety signs.

GdSr₂AlO₅:Yb³⁺/Er³⁺ micro-particles were synthesized by a simple solid state method.     

Aerosol synthesis of TiO2:Er3+/Yb3+ submicron-sized spherical particles and upconversion optimization for application as anti-counterfeiting materials

Er³⁺/Yb³⁺-doped TiO₂ up-conversion (UC) phosphors were prepared by spray pyrolysis, and the UC luminescence properties were optimized by changing the calcination temperature and the concentration of Er³⁺ and Yb³⁺ dopants. TiO₂:Er³⁺/Yb³⁺ showed green and red emissions due to the ²H_11/2/⁴S_3/2 → ⁴I_15/2 transition and the ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺ ions, respectively. The R/G ratio between red (R) and green (G) emissions does not change significantly with Er concentration but increases linearly with increasing Yb³⁺ concentration. The dependence of UC luminescence intensity on 980 nm IR pumping power showed that both the red and green UC luminescence of TiO₂:Er³⁺/Yb³⁺ occurred through a typical two-photon process. In terms of achieving the highest red UC emission intensity, the optimal Er³⁺ and Yb³⁺ contents are 0.3% and 7.0%, respectively. The UC intensity of TiO₂:Er³⁺/Yb³⁺ particles increases until they are calcined at temperatures up to 600 °C and then decreases rapidly above 800 °C. This is because when the calcination temperature is 800 °C and higher, not only does the phase transition of TiO₂:Er³⁺/Yb³⁺ occur from anatase to rutile, but also the Yb₂Ti₂O₇ impurity phase is formed. According to SEM and TEM/EDX analysis, the prepared TiO₂:Er³⁺/Yb³⁺ UC powders have an average particle size of 680 nm, a spherical shape with a dense structure, and Er and Yb are uniformly dispersed throughout the particles without local separation. A mark prepared using TiO₂:Er³⁺/Yb³⁺ powder was found to have a UC emission high enough to be visually observed when irradiated with a portable 980 nm IR lamp.

TiO₂:Er/Yb spherical particles were synthesized by spray pyrolysis and their luminescence was optimized for application as anti-counterfeiting materials.     

Supercapacitive performance of TiO2 boosted by a unique porous TiO2/Ti network and activated Ti3+

TiO₂ has been reported to have considerable capacity through appropriate surface modification. Previous studies of TiO₂-based supercapacitors mainly focused on anodized TiO₂ nanotubes and TiO₂ powder, even though the capacitance still lags behind that of carbon-base materials. In this work, a three-dimensional porous TiO₂/Ti (PTT) network was constructed by anodic oxidation and its capacitance was boosted by subsequent aluminum-reduction process. Activated Ti³⁺ was proved to be being successfully introduced into the surface of pristine PTT, resulting in the prominent enhancement of supercapacitive performance. An areal capacitance of 81.75 mF cm⁻² was achieved from Al-reduced PTT (Al-PTT) at 500 °C in 1 M H₂SO₄ electrolyte, which was among the highest value of pure TiO₂-based electrodes. Good electrochemical stability was also confirmed by the 3.12% loss of the highest capacity after 5000 CV cycles. More importantly, the activated Ti³⁺/Ti⁴⁺ redox couple in modified TiO₂ is solidly confirmed by being directly observed in CV curves. The capacitive mechanism of the redox reaction is also studied by electrochemical tests. The construction of a 3D porous network structure and efficient Ti³⁺ introduction provide an effective method to boost the supercapacitive performance of TiO₂-based materials for energy storage applications.

Excellent supercapacitive performance is achieved by constructing a 3D porous TiO₂/Ti network structure and introducing an activated Ti³⁺/Ti⁴⁺ redox couple.     

ALD Al2O3 gate dielectric on the reduction of interface trap density and the enhanced photo-electric performance of IGO TFT

The amorphous indium gallium oxide thin film transistor was fabricated using a cosputtering method. Two samples with different gate dielectric layers were used as follows: sample A with a SiO₂ dielectric layer; and sample B with an Al₂O₃ dielectric layer. The influence of the gate dielectrics on the electric and photo performance has been investigated. Atomic layer deposition deposited the dense film with low interface trapping density and effectively increased drain current. Therefore, sample B exhibited optimal parameters, with an I_on/I_off ratio of 7.39 × 10⁷, the subthreshold swing of 0.096 V dec⁻¹, and μ_FE of 5.36 cm² V⁻¹ s⁻¹. For ultraviolet (UV) detection, the UV-to-visible rejection ratio of the device was 3 × 10⁵, and the photoresponsivity was 0.38 A W⁻¹ at the V_GS of −5 V.

The amorphous indium gallium oxide thin film transistor was fabricated using a cosputtering method.     

Dielectric and photoluminescence properties of fine-grained BaTiO3 ceramics co-doped with amphoteric Sm and valence-variable Cr

(Ba_1−xSm_x)(Ti_1−xCr_x)O₃ (BSTC) and (Ba_1−xSm_x)(Ti_{1−(x−0.01)}Cr_x−0.01)O₃ (BSTC1) ceramics with a single-phase perovskite structure were prepared using a traditional solid state based method. The structure, microstructure, site occupations, valence states of Cr, photoluminescence, and dielectric properties of these ceramics were investigated using XRD, SEM, EDXS, RS, EPR, XPS, and dielectric measurements. All ceramics exhibit a fine-grained microstructure (0.7 μm). Three valence states of Cr ions were confirmed and Cr predominates as Cr³⁺ enter the Ti⁴⁺ sites with a stronger EPR signal (1.974). The RS bands of high-wavenumber were attributed to photoluminescence from Sm³⁺ ions. The formation of defect complexes play leading roles in the removal of prevent the grain growth, and photoluminescence quenching. (Ba_1−xSm_x)(Ti_{1−(x−0.01)}Cr_x−0.01)O₃ (BSTC1) ceramics with amphoteric Sm³⁺ ions exhibit a regular diffuse phase transition behavior, rapid T_m-shifting rate of −24.3 °C/at% (Sm/Cr), higher lower tan δ and x = 0.04 and 0.05 met the EIA Y5V specification.

(Ba_1−xSm_x)(Ti_1−xCr_x)O₃ (BSTC) and (Ba_1−xSm_x)(Ti_{1−(x−0.01)}Cr_x−0.01)O₃ (BSTC1) ceramics with a single-phase perovskite structure were prepared using a traditional solid state based method.     

The preparation,microstructure and mechanical properties of a dense MgO–Al2O3–SiO2 based glass-ceramic coating on porous BN/Si2N2O ceramics

A dense MgO–Al₂O₃–SiO₂ based glass-ceramic coating was prepared by a doctor blade process on a porous BN/Si₂N₂O ceramic surface followed by heat treatment at 1050 °C under nitrogen flow. The phase composition, microstructure, mechanical properties and water absorption of the coating were studied. The coating consisted of α-cordierite phase with a small amount of glass phase. The dense coating without pores and cracks was favorable to seal and densify the porous ceramic surface due to part of the molten glass infiltrating the surface pores. The coating was defect-free and tightly bonded to the substrate because of a larger bonding area between the coating and the substrate. The elastic modulus and bending strength of the glass-ceramic coating were 37.9 GPa and 67.1 MPa, respectively. Moreover, the coated samples had a high Vickers hardness and low water absorption.

A dense MgO–Al₂O₃–SiO₂ based glass-ceramic coating was prepared by a doctor blade process on a porous BN/Si₂N₂O ceramic surface followed by heat treatment at 1050 °C under nitrogen flow.     

Luminescence properties,energy transfer and thermal stability of white emitting phosphor Sr3(PO4)2:Ce3+/Tb3+/Mn2+ for white LEDs

A series of Sr₃(PO₄)₂:Ce³⁺/Mn²⁺/Tb³⁺ phosphors were synthesized by a high temperature solid phase method. After introducing Ce³⁺ as sensitizer in Sr₃(PO₄)₂:Ce³⁺/Mn²⁺, the efficient energy transfer from Ce³⁺ to Mn²⁺ was observed and analyzed in detail, and Sr₃(PO₄)₂:Ce³⁺/Mn²⁺ was demonstrated to be color tunable, changing from blue to orange red. In addition, Tb³⁺ ion, which mainly emits green light, was further added into the Sr₃(PO₄)₂:Ce³⁺/Mn²⁺. Due to the addition of this green emission, the white emitting phosphors with good quality were obtained. At the same time, the energy transfer mechanisms among Ce³⁺, Tb³⁺ and Mn²⁺ ions were also analyzed in detail. The results show that Sr₃(PO₄)₂:Ce³⁺/Mn²⁺/Tb³⁺ is a promising candidate for white light emitting diodes.

The tunable emission phosphor was realized by the energy transfer.     

Luminescence properties of ZnGa2O4:Cr3+,Bi3+ nanophosphors for thermometry applications

Chromium(iii) and bismuth(iii) co-doped ZnGa₂O₄ nanoparticles are synthesized by a hydrothermal method assisted by microwave heating. The obtained nanoparticles, with a diameter smaller than 10 nm, present good luminescence emission in the deep red range centered at 695 nm after coating with a silica layer and calcination at 1000 °C during 2 h. Persistent luminescence and photoluminescence properties are investigated at several temperatures. Bandwidth and luminescence intensity ratio of persistent emission do not present enough change with temperature to obtain a competitive nanothermometer with high sensitivity. Nevertheless, persistent luminescence decay curves present a significant shape change since the trap levels involved in the deexcitation mechanism are unfilled with increase of temperature. Even if the sensitivity reaches 1.7% °C⁻¹ at 190 °C, the repeatability is not optimal. Furthermore, photoluminescent lifetime in the millisecond range extracted from the photoluminescence decay profiles drastically decreases with temperature increase. This variation is attributed to the thermal equilibrium between two thermally coupled chromium(iii) levels (²E and ⁴T₂) that have very different deexcitation lifetimes. For ZnGa₂O₄:Cr³⁺_0.5%,Bi³⁺_0.5%, the temperature sensitivity reaches 1.93% °C⁻¹ at 200 °C. Therefore, this kind of nanoparticle is a very promising thermal sensor for temperature determination at the nanoscale.

Luminescence properties of chromium(iii) and bismuth(iii) co-doped ZnGa₂O₄ nanoparticles are investigated for thermometry applications.     

Influence of Al2O3 nanoparticle doping on depolarization temperature,and electrical and energy harvesting properties of lead-free 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 ceramics

In this research article, the effects of Al₂O₃ nanoparticles (0–1.0 mol%) on the phase formation, microstructure, dielectric, ferroelectric, piezoelectric, electric field-induced strain and energy harvesting properties of the 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ (BNT–6BT) ceramic were investigated. All ceramics have been synthesized by a conventional mixed oxide method. The XRD and Raman spectra showed coexisting rhombohedral and tetragonal phases throughout the entire compositional range. An increase of the grain size, T_F–R, T_m, ε_max and δ_A values was noticeable when Al₂O₃ was added. Depolarization temperature (T_d), which was determined by the thermally stimulated depolarization current (TSDC), tended to increase with Al₂O₃ content. The good ferroelectric properties (P_r = 32.64 μC cm⁻², E_c = 30.59 kV cm⁻¹) and large low-field d₃₃ (205 pC N⁻¹) values were observed for the 0.1 mol% Al₂O₃ ceramic. The small Al₂O₃ additive improved the electric field-induced strain (S_max and ). The 1.0 mol% Al₂O₃ ceramic had a large piezoelectric voltage coefficient (g₃₃ = 32.6 × 10⁻³ Vm N⁻¹) and good dielectric properties (ε_r,max = 6542, T_d = 93 °C, T_F–R = 108 °C, T_m = 324 °C and δ_A = 164 K). The highest off-resonance figure of merit (FoM) for energy harvesting of 6.36 pm² N⁻¹ was also observed for the 1.0 mol% Al₂O₃ ceramic, which is suggesting that this ceramic has potential to be one of the promising lead-free piezoelectric candidates for further use in energy harvesting applications.

In this research article, the effects of Al₂O₃ nanoparticles (0–1.0 mol%) on the phase, microstructure, dielectric, ferroelectric, piezoelectric, electric field-induced strain and energy harvesting of the BNT–6BT ceramic were investigated.