Binary transparent (Ho1-xDyx)2O3 ceramics: Compositional influences on particle properties,sintering kinetics and Faraday magneto-optical effects

Binary transparent magneto-optical (Ho_1-xDy_x)₂O₃ (x = 0.01–1) ceramics derived from layered rare-earth hydroxide (LRH) compounds were fabricated by vacuum sintering. They have in-line transmittances of ～67?77 % at the visible wavelength of 700 nm and ～77?84 % at the mid-infrared wavelength of 5 μm with similar maximal infrared cut-off at ～9.5 μm. The impacts of Dy³⁺ doping on particle properties, sintering kinetics and Faraday magneto-optical effects were systematically investigated. The results show that (1) The LRH precursors exhibit the nanosheet morphology with the thickness of ～6?10 nm. Dy³⁺ incorporation not only induces an expansion for the hydroxide host layer but also a contracted interlayer distance; (2) Upon calcination at 1100 °C, the LRH nanosheets collapse into sphere-like oxide particles. The addition of Dy³⁺ leads to increasing lattice constants and decreasing theoretical densities for the (Ho,Dy)₂O₃ solid solutions; (3) A smaller bandgap energy for Dy₂O₃ (～4.85 eV) was obtained relative to those of (Ho_0.9Dy_0.1)₂O₃ (～5.24 eV) and Ho₂O₃ (～5.31 eV); (4) Dy³⁺ dopant promotes grain growth and the pure Dy₂O₃ bulk has a rather smaller grain-boundary-diffusion controlled activation energy (～457 kJ/mol) than the (Ho_0.9Dy_0.1)₂O₃ counterpart (～626 kJ/mol); (5) The Verdet constants of magneto-optical (Ho_1-xDy_x)₂O₃ ceramics generally linearly increase with the rise of Dy³⁺ concentration.     

Synthesis and luminescence characterization of Pr3+, Gd3+ co-doped SrF2 transparent ceramics

Pr³⁺, Gd³⁺ co-doped SrF₂ transparent ceramic, as the potential material for visible luminescent applications, was prepared by hot-pressing of precursor nanopowders. The microstructure, phase compositions, and in-line transmittance, as well as the photoluminescence properties were investigated systematically. Highly optical quality Pr,Gd:SrF₂ transparent ceramic with nearly pore-free microstructure was obtained at 800°C for 1.5 hours. The average in-line transmittance of the x at.% Pr, 6 at.% Gd:SrF₂ (x = 0.2, 0.5, 1.0, 2.0) transparent ceramics reached to 87.3 % in the infrared region. The photoluminescence spectra presented intense visible light emissions under the excitation of 444 nm, the main intrinsic emission bands located at 483 and 605 nm, which were attributed to the transitions of Pr³⁺: ³P₀ → ³H₄ and ¹D₂ → ³H₄, respectively. With the co-doping of Gd³⁺ ions, the emission intensity of the Pr:SrF₂ transparent ceramic was greatly enhanced. All the emission bands of x at.% Pr, 6 at.% Gd:SrF₂ transparent ceramics exhibited the highest luminescence intensity with the 1.0 at.% Pr³⁺ doping concentrations, whereas the lifetimes decreased dramatically with the Pr³⁺ doping contents increasing from 0.2 to 2.0 at.% due to its intense concentration quenching effect. The 1 at.% Pr, 6 at.% Gd:SrF₂ transparent ceramic is a promising material for visible luminescent device applications.     

Nickel element doping impacts on structure features and Faraday effects of magneto-optical transparent holmium oxide ceramics

The nickel element doped holmium oxide (Ho₂O₃:Ni) transparent magneto-optical ceramics were fabricated by vacuum sintering and the dopant impacts on structure features and Faraday effects were investigated. The starting oxide powders were synthesized by pyrolyzing the resulting layered holmium-based hydroxide nanosheets prepared from a chemical precipitation route using the sodium hydroxide as precipitant at the freezing temperature. Upon high-temperature sintering, the ${\mathrm{Ni}}_i^{••}$ defect is introduced by Ni²⁺ substitution for Ho³⁺ to form the interstitial solid solution. The 1 at.% Ni²⁺ doped Ho₂O₃ ceramic sample exhibits an in-line transmittance of ∼70.04% at 1 550 nm with a relative density of ∼99.88%, while more Ni²⁺ incorporation (e.g., 2‒5 at.%) even leads to a completely opaque state. The magneto-optical transparent Ho₂O₃:1%Ni ceramic developed in this work has Verdet constants of ∼−195, −65, and −29 rad/(T·m) at 635, 1 064, and 1 550 nm, respectively, which are ∼1.8-fold higher than the commercial terbium gallium garnet crystal or ∼1.4-fold higher than the pure Ho₂O₃ ceramic. This material also possesses relatively large figure of merit of ∼14.6°/T at 1 064 nm and relatively high thermal conductivity of ∼7.5 W/(m·K) at room temperature.     

Fabrication,microstructure and optical characterizations of holmium oxide (Ho2O3) transparent ceramics

Ho₂O₃ transparent ceramics were fabricated by vacuum pre-sintering combined with hot isostatic pressing (HIP) post-treatment at relatively low temperature from high-purity Ho₂O₃ powder calcined at 1000 °C for 4 h. The optimal Ho₂O₃ ceramic sample prepared by vacuum pre-sintering at 1250 °C and HIP post-treating at 1450 °C has a dense microstructure with average grain size of 0.77 μm, and the in-line transmittances reach 80.7 % at 1550 nm and 76.7 % at 1064 nm. The effect of air annealing on the optical quality of Ho₂O₃ ceramics was studied, and the existence of compressed pores in the HIP-ed Ho₂O₃ ceramics was confirmed. The Verdet constants of Ho₂O₃ ceramics were measured to be -47.4 rad/(T m at 1064 nm and -15.4 rad/(T m at 1561 nm. High transmittance and large Verdet constant in the wavelength regions 1–1.07 μm, 1.3–1.5 μm make Ho₂O₃ transparent ceramics promising for magneto-optical devices for lasers based on Yb-, Nd-doped materials and telecom lasers.     

Photoluminescence and energy transfer of Lu3Al5O12:Ce3+, Pr3+ phosphors

Ce³⁺ and Pr³⁺ co?doped Lu₃Al₅O₁₂ phosphors were synthesized by the sol–gel process, and their crystal structure, photoluminescence (PL) properties, and energy transfer (ET) from the Ce³⁺ to Pr³⁺ were studied. The Lu_2.94?yAl₅O₁₂:0.06Ce³⁺, yPr³⁺ phosphors (0.002 ≤ y ≤ 0.008) showed the green?yellow emission from the ²D_3/2 → ²F_{5/2, 7/2} transition of Ce³⁺ and the red emission at 610 and 637 nm, which were caused by the ¹D₂→³H₄ and ³P₀→³H₅ transitions of Pr³⁺, respectively. The optimal concentration of Pr³⁺ for efficient ET was found to be x = 0.006. The electric quadrupole?quadrupole interaction was responsible for the concentration quenching in the Lu_2.94?yAl₅O₁₂:0.06Ce³⁺, yPr³⁺ phosphors, based on Dexter's theory. The incorporation of Pr³⁺ for Lu³⁺ enhanced the red PL intensity in the Lu_2.94Al₅O₁₂:0.06Ce³⁺ phosphor.     

Multiplicity of photoluminescence in Raman spectroscopy and defect chemistry of (Ba1−xRx)(Ti1−xHox)O3 (R = La,Pr, Nd,Sm) dielectric ceramics

(Ba_1?xR_x)(Ti_1?xHo_x)O₃ (R = La, Pr, Nd, Sm; x ≥ 0.04) (BRTH) ceramics were prepared using a mixed oxides method. The solubility limits in BRTH with R = La, Pr, Nd, Sm were determined by XRD to be x = 0.11, 0.12, 0.06, and 0.14, respectively. The ionic radius of R at Ti-site plays a decisive role in the solubility limit in BRTH. Only BRTH with R = La satisfied Vegard's law. The multiplicity of photoluminescence (PL) signals of Nd³⁺/Ho³⁺ and Sm³⁺/Ho³⁺ in Raman scattering under 532-nm excitation laser and the high-permittivity abnormality for the denser BRTH with R = Sm and at x = 0.07 were reported. The PL provided the evidence of a small number of Ho³⁺ at Ba-site in BRTH and it was determined that the number of Ba-site Ho³⁺ ions increased from 0.05 at% at R = La to 0.19 at% at R = Sm with increasing atomic number of light rare earth. BRTH exhibited a much broadened dielectric-temperature characteristics, marked by ×5 T, ×6 T, ×7 T, and ×8 S dielectric specifications for BRTH with R = La, Pr, Nd, Sm and at x = 0.06, respectively, and they exhibited lower dielectric loss (tan δ < 0.015) at room temperature. The dielectric-peak temperature (T_m) of BRTH decreased linearly at a rate of less than ?21 °C/%(R/Ho). The defect chemistry, solubility limit, lower dielectric loss, and dielectric abnormality are discussed.     

Fabrication of 4 at.% La3+ ion doped (TbxLu0.96−x)2O3 transparent ceramics by using NC-PLSH technology and characterisation of their magneto-optical properties

Nanocrystalline powders and pressureless sintering (NC-PLSH) were used in a H₂ atmosphere to fabricate 4 at.% La³⁺ doped (Tb_xLu_0.96?x)₂O₃ magneto-optical transparent ceramics. La³⁺ was utilised as a sintering aid, and Lu³⁺ was used as a phase stabiliser. A component of the (Tb_xLu_0.96?xLa_0.04)₂O₃ magneto-optical material was designed and investigated based on powder sinterability and green compact sintering. Transparent (Tb_xLu_0.96?xLa_0.04)₂O₃ ceramics were obtained by using a one-step sintering process in H₂ atmosphere, without the need for subsequent hot isostatic pressing. The in-line transmittance of the as-polished 4 at.% La³⁺:(Tb_0.8Lu_0.16)₂O₃ ceramic was 79% at 1400 nm. The measured Verdet constant at wavelengths of 633 nm and 1064 nm was 354 rad/(T·m) and 100.2 rad/(T·m), respectively. The required length of the (Tb_0.8Lu_0.16La_0.04)₂O₃ ceramics was 63% less than that of Tb₃Ga₅O₁₂ ceramics.     

High piezoelectric coefficient of Pr2O3-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics

Pr₂O₃-doped Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCTZ-xPr) ceramics were prepared by the conventional solid-state method. A tetragonal phase is only observed in these ceramics, and the introduction of Pr₂O₃ decreases their sintering temperature without affecting negatively the piezoelectric constant. Enhanced ferroelectric properties were obtained in these BCTZ-xPr ceramics. The ceramic with x=0.06 wt% exhibits a good electrical behavior of d₃₃∼460 pC/N, k_p∼47.6%, ε_r∼4638, and tan δ∼0.015 when sintered at a low temperature of ∼1400 °C. As a result, the BCTZ-xPr ceramic is a promising candidate for lead-free piezoelectric ceramics.     

Synthesis and characterization of PrxZr1-xSiO4 (x = 0–0.08) yellow pigments via non-hydrolytic sol-gel method

Yellow inorganic pigments Pr_xZr_1-xSiO₄ (x?=?0–0.08) have been prepared by a novel non-hydrolytic sol-gel (NHSG) method at 750?°C for 2?h. Replacing Pr⁴⁺ for Zr⁴⁺ in ZrSiO₄ increased the cell volume and changed the color from white to yellow gradually. The Si―O―Zr and Si―O―Pr bands were observed in the FT-IR spectra of xerogel, indicating it could reach homogeneous mixing at the atomic level. Therefore, it promoted the solid solution reaction between Pr and zircon at low temperature. The samples exhibit high doping limitation (x?=?0.08) and brilliant yellow hue (b^*?=?69.48) in contrast with the previously reported praseodymium zircon yellow pigments. The intense of yellow hue was increased with increasing the Pr doping content due to the increase of Pr⁴⁺/Pr³⁺ species. After applying on bisque ceramic tiles, the pigment exhibited excellent coloration, high thermal stability and low solubility in molten glazes, indicating its potential application in ceramic decoration.     

Influence of Cr3+ substitution for Mg2+ on the crystal structure and microwave dielectric properties of CaMg1-xCr2x/3Si2O6 ceramics

The CaMg_1-xCr_2x/3Si₂O₆ (0?≤?x?≤?0.1) microwave dielectric ceramics were synthesized via conventional solid state reaction. In this study, the effects of Cr³⁺ substituting for Mg²⁺ on morphology, crystal structure and microwave dielectric properties of CaMg_1-xCr_2x/3Si₂O₆ ceramics were explored. XRD diffraction patterns exhibited that the CaMg_1-xCr_2x/3Si₂O₆ ceramics possessed the pure phase of CaMgSi₂O₆ when x?≤?0.06 and a small amount of secondary phase Ca₃Cr₂(SiO₄)₃ for 0.08?≤?x?≤?0.1. SEM micrographs revealed that the substitution of Mg²⁺ with Cr³⁺ could decrease the grain size. The apparent density was affected by the concentration of Mg vacancies. The correlation between crystal structure and microwave dielectric properties was investigated through the Rietveld refinement and Raman analysis. The microwave dielectric properties were mainly dependent on relative density, ionic polarizabilities, internal strain ?, disordered structure and MgO₆ octahedron distortions. Finally, CaMg_1-xCr_2x/3Si₂O₆ (x?=?0.02) ceramics sintered at 1270?°C for 3?h exhibited excellent microwave dielectric properties of ε_r?=?8.06, Q?×?f?=?89054?GHz, τ_f?=??44.92182?ppm/ºC.     

Fluorescence intensity ratio (FIR) analysis of the temperature sensing properties in transparent ferroelectric PMN-PT:Pr3+ ceramic

A transparent ferroelectric 0.75Pb(Mg_1/3Nb_2/3)O₃-0.25PbTiO₃:0.015Pr³⁺ ceramic was synthesized and its temperature-sensing ability was investigated based on the fluorescence intensity ratio (FIR) method. The transparency was found to be of the order of 68% at 900 nm for a sample thickness of 0.7 mm, comparable to the theoretical value of ~71%, benefiting the photoluminescence of the Pr³⁺ ions inside the ceramic. Instead of the traditional Boltzmann exponential style and varying sensitivity, a highly linear temperature response was obtained for the studied ceramic. Further, a constant FIR sensitivity of 0.70 %K^-1 was achieved over the temperature range of -50–40 °C, making the ceramic suitable for thermometry at room temperature and below.     

Preparation and characterization of transparent magneto-optical Ho2O3 ceramics

Transparent magneto-optical Ho₂O₃ ceramics were successfully prepared with an in-line transmittance of ~73% at the wavelength of 1000 nm (~90% of the theoretical transmittance of Ho₂O₃ single crystal) and an average grain size of ~28 μm. The ceramics were fabricated using sulfate-exchanged nitrate-type layered rare-earth hydroxide as the precipitation precursor at a relatively low sintering temperature of 1700°C. The layered compound exhibited nanosheet morphology and fully collapsed into a round oxide powder with an average particle size of ~48 nm by pyrolysis. Calcination temperature for Ho₂O₃ powder significantly affected the optical quality of the sintered body and the optimum calcination temperature was found to be 1050°C. The transparent magneto-optical Ho₂O₃ ceramics displayed wavelength-dependent Verdet constants of −180, −46, and −20 rad/Tm at 632, 1064, and 1550 nm, respectively. Thus, the Ho₂O₃ ceramics show good potential for applications in high-power laser systems.     

Enhancement in CO oxidation activity of nanosized CexZr1−xO2 solid solutions by incorporation of additional dopants

The influence of Hf, Pr and Tb dopant cations on structural and catalytic properties of nanosized Ce_xZr_1?xO₂ solid solutions has been investigated. A wide range of analytical techniques are utilized to characterize the synthesized materials, and the catalytic activity is evaluated for CO oxidation. XRD, Raman, SEM and TEM results suggested formation of dopant cation incorporated ceria–zirconia solid solutions with highly homogeneous morphology and lattice defects. The CO-TPR measurements revealed an enhanced reducibility of Ce_xZr_1?xO₂ which is reflected in their better catalytic activity. The role of Tb⁴⁺/Tb³⁺ and Pr⁴⁺/Pr³⁺ redox couples in facilitating a higher activity has been addressed.     

Study of the relationships among the crystal structure,phase transition behavior and macroscopic properties of modified (K,Na)NbO3-based lead-free piezoceramics

Although phase boundary engineering has made notable progress in improving the electrical properties of (K,Na)NbO₃-based piezoceramics, lattice distortion and spontaneous polarization of multiphase coexisting systems are a few of the remaining concerns. Here, new research employing XRD Rietveld refinement was performed to explore crystal structures, phase fractions and atomic parameters of Fe₂O₃-added (0.995-x)K_0.48Na_0.52NbO₃-xBi_0.5Na_0.5ZrO₃-0.005BiScO₃ ceramics. The distortion of the oxygen octahedron and the spontaneous polarization were presented. Central cation displacement provides a much larger contribution to polarization and the electric dipole moment in orthorhombic phase is much larger than that in tetragonal phase. Benefiting from tetragonal-orthorhombic phase coexistence and lattice distortion, optimized ferroelectric and piezoelectric properties (d₃₃?～?381?pC/N, P_r?～?20.47?μC/cm²) were obtained. The ceramic still holds a large d₃₃ (313?pC/N) after up to 300?℃ of thermal annealing. A series of material constants was also calculated and compared to lead-based ones.     

Electro-morphological,structural, thermal and ionic conduction properties of Gd/Pr co-doped ceria electrolytes exhibiting mixed Pr3+/Pr4+ cations

Gd_0.2-xPr_xCe_0.8O_1.90, (x?=?0, 0.02, 0.04, 0.06, 0.08, 0.10) has been synthesized by means of a simple co-precipitation route based on ammonium carbonate as the precipitating agent. The as-synthesized precursors are cerium-gadolinium-praseodymium amorphous hydroxycarbonates, which are nanometric in size with highly homogeneous morphology, leading to reactive doped and co-doped nanocrystalline (≈13?nm) ceria after a mild thermal treatment (2?h at 600?°C). The obtained results highlight the very positive effect of Pr on the powders’ sintering behaviour, which favour a better densification of the final pellets, thus improving both their microstructure (with relative densities of 97–99% after sintering at 1250?°C for 3?h) and electrochemical properties (up to 1.25·10–1?S?cm^?1 at 800?°C for sample 6Pr) compared to the state-of-art ceria-based electrolytes. Through a comprehensive characterization, a relation was formed between the Pr content and the microstructural features of the sintered pellets and their electrical behaviour. The amount of Pr doping was investigated over a wide range and 6?mol% has been established to be optimal (possessing the lowest electronic conductivity contribution). Definitely, these results indicate that Gd_0.2-xPr_xCe_0.8O_1.90 has an excellent set of characteristics, both microstructural and electrical, and a convenient fabrication process, thus making it perfectly suitable for IT-SOFC practical applications.     

Effect of Pr on the electrical and chemical properties of cerium oxide prepared by combustion method

Nanoparticles of Ce_1−xPr_xO₂ (X: 0.6 and 0.8), were synthesized by the combustion method using citric acid as chelating and fuel agent. The X-ray diffraction patterns and Rietveld refinements confirm that samples shown as a single phase in a cubic fluorite structure, with an increase in the lattice parameter as a function of Pr concentration. The crystallite size domains obtained by the Scherrer formula, confirm values around 10 and 37 nm. The scanning electron microscopy images, show that the solids are composed of dense heterogeneous aggregates. The X-ray photoelectron spectroscopy, reveals that oxides are composed of cerium and praseodymium cations in oxidation states 4+ and 3+ respectively. The TPR-H₂ profiles indicate that cerium and praseodymium cations present in the obtained systems are completely reduced to Ce³⁺ and Pr³⁺ at temperatures above 790°C. The impedance spectroscopy data at room temperature showed that the conduction processes for the two systems take place at the grain boundaries. The Ce_0.2Pr_0.8O₂ system offer lower resistance, due to the high amount of Pr³⁺ ions inserted in the structure and the high amount of oxygen vacancies formed in the synthesis process.     

Large electrostrictive effect and high energy storage performance of Pr3+-doped PIN-PMN-PT multifunctional ceramics in the ergodic relaxor phase

The photoluminescence, dielectric relaxation, ferroelectric hysteresis, and field-induced strain properties of Pr³⁺-doped 0.24Pb(In_1/2Nb_1/2)O₃-0.42Pb(Mg_1/3Nb_2/3)O₃-0.34PbTiO₃ (PIN-PMN-PT:Pr³⁺) multifunctional ceramics have been investigated. It was found that Pr³⁺ doping enhanced the dielectric diffuseness and relaxation behavior of PIN-PMN-PT ceramics. Slim P-E loops and S-E curves appear in PIN-PMN-PT:Pr³⁺ ceramics when the Pr³⁺ doping concentration reaches 1.4 mol%. Local domain configurations associated with phase transitions were investigated by piezoresponse force microscopy (PFM). Large electrostrictive coefficient Q₃₃ (?0.03 m⁴/C²) and high energy-storage efficiency η (92%) were obtained in 2 mol% Pr³⁺-doped PIN-PMN-PT ceramic in the ergodic relaxor (ER) phase at room temperature. The giant electrostrictive effect and excellent energy-storage performance are related to the field-induced dynamic behavior of polar nanoregions (PNRs). The results show that the PIN-PMN-PT:Pr³⁺ system is an excellent multifunctional material for making electromechanical and energy storage devices.     

Pr3+/Yb3+:PLZT ferroelectric ceramics for near‐infrared radiation at 1340 nm

The near‐infrared luminescence properties of Pr³⁺/Yb³⁺:PLZT ferroelectric ceramics have been examined for the first time. Independently, upon either 450 nm (Pr³⁺) or 980 nm (Yb³⁺) excitation, luminescence centered at 1340 nm was observed, which corresponds to the ¹G₄→³H₅ transition of Pr³⁺. Several spectroscopic parameters for the ¹G₄→³H₅ transition of Pr³⁺ ions were determined. The average product of emission cross section and radiative lifetime were relatively large for all x/65/35 PLZT samples (x=6‐10) studied, with values close to 105±2 (×10^?26 cm²·s). These spectroscopic investigations indicate that Pr³⁺/Yb³⁺:PLZT ferroelectric ceramics are promising candidate for efficient sources emitting near‐infrared radiation at 1340 nm.     

Combining high energy efficiency and fast charge-discharge capability in novel BaTiO3-based relaxor ferroelectric ceramic for energy-storage

Compared with the other types of ceramic capacitors, relaxor ferroelectric ceramics demonstrate superior potential in energy-storage fields due to their higher energy efficiency, faster charge-discharge rate, and better temperature stability. In this study, we designed and synthesized a novel high performance BaTiO₃-based ((1-x)BaTiO₃-xBi(Ni_2/3Nb_1/3)O₃, x?=?0.08, 0.10, 0.12, and 0.14) energy-storing ceramics through ferroelectric properties modulation, which display typical relaxor characteristics. The optimum energy storage properties, i.e. ultrahigh energy efficiency (95.9%), high energy-storage density (2.09?J?cm^?3) and good temperature stability (the fluctuations in energy-storage properties are less than 5% over 20–120?°C) are obtained at x?=?0.12 (0.88BT-0.12BNN). The 0.88BT-0.12BNN relaxor ferroelectric ceramic demonstrates obviously superior comprehensive energy-storage properties than most of other unleaded ceramics. Besides, investigation efforts were also spent on the pulsed charge-discharge performance of the 0.88BT-0.12BNN ceramic to evaluate its feasibility as energy-storage devices. More importantly, the 0.88BT-0.12BNN ceramic also exhibits outstanding charge-discharge performance with fast discharge rate (t_0.9 <?100?ns), a high level of power density (36.9?MW?cm^?3), and good temperature stability. These excellent performance parameters qualify this novel and environmentally friendly BaTiO₃-based ceramic as a promising alternative option in energy-storage section. Meanwhile, this study also provides an effective approach to attain high energy-storage density as well as energy efficiency in BaTiO₃-based relaxor ferroelectric ceramics.     

Improved non-ohmic and dielectric properties of Cr3+ doped CaCu3Ti4O12 ceramics prepared by a polymer pyrolysis solution route

CaCu_3-xCr_xTi₄O₁₂ (x?=?0.00–0.20) ceramics were prepared via a polymer pyrolysis solution route. Their dielectric properties were improved by Cr³⁺ doping resulting in an optimal dielectric constant value of 7156 and a low tanδ?value of 0.092 in a sample with x?=?0.08. This might have resulted from a decrease in oxygen vacancies at grain boundaries. XANES spectra confirmed the presence of Cu⁺ ions in all ceramic samples with a decreasing Cu⁺/Cu²⁺ ratio due to an increased content of Cr³⁺ ions. All CaCu_3-xCr_xTi₄O₁₂ ceramics showed nonlinear characteristic with improvement in both the breakdown field (E_b) and its nonlinear coefficient (α). Interestingly, the highest values of α, ～ 114.4, and that of E_b, ～8455.0?±?123.6?V?cm^?1, were obtained in a CaCu_3-xCr_xTi₄O₁₂ sample with x?=?0.08. The improvement of dielectric and nonlinear properties suggests that they originate from a reduction of oxygen vacancies at grain boundaries.