Room-temperature multiferroic properties of Al-doped hexaferrites sintered at high oxygen atmospheric concentrations

The room-temperature magnetoelectric effects of Al-doped polycrystalline hexaferrites Sr₃Co₂(Fe_1-xAl_x)₂₄O₄₁(x = 0.00, 0.02, and 0.04) sintered under high oxygen atmospheric concentrations were comprehensively investigated. The magnetic phases and magnetic structures were modulated by high sintering oxygen atmospheric concentrations as demonstrated by M-T tests and magnetic hysteresis loops. Compared with previous specimens sintered under low oxygen atmospheric concentrations, the transverse conical spin structures of the Sr₃Co₂(Fe_1-xAl_x)₂₄O₄₁(x = 0.00, 0.02, and 0.04) were obviously strengthened by high sintering oxygen atmospheric concentrations, exhibiting magnetoelectric effects in high magnetic field ranges (>1 T).     

Effect of substitution of La3+ on structural and electrical properties of Sr(Fe0.5Nb0.5)O3 ceramic

In this work, we have mainly reported the effect of lanthanum substitution on structural, dielectric, impedance and transport properties of strontium iron niobate (i.e., Sr_1-xLa_x(Fe_0.5Nb_0.5)_1-x/4O₃ (x = 0, 0.05, 0.1, 0.15, 0.2)). The materials were synthesized using standard ceramic technology. The preliminary structural analysis was done by using the room temperature X-ray diffraction data. The samples of higher concentrations (x = 0.15 and x = 0.20) show the development of an additional phase (i.e., LaNbO₄ and Sr₃La₄O₉). Studies of frequency and temperature dependence of dielectric parameters exhibit an anomaly and relaxor behavior in the compounds. The electrical impedance and modulus analysis of frequency and temperature-dependent data show the contributions of grains and grain boundaries in the resistive and capacitive properties of the compounds. The study of transport properties of AC conductivity has provided the conduction and relaxation mechanism. The substitution of La³⁺ has significantly changed the dielectric constant, tangent loss, and transport properties of the material.     

Insight of structural,dielectric and spectroscopic characteristics of Ba0.6Sr0.4-xYbxFe12-yCoyO19 M-type hexaferrite

Ba_0.6Sr_0.4-xYb_xFe_12-yCo_yO₁₉, (0.0≤x ≤ 0.125, 0.0≤y ≤ 1.25) M-type hexaferrite were synthesized using the auto combustion sol-gel process. The synthesized samples were then sintered at 1200 °C for 5 h in a muffle furnace. XRD, FTIR, Raman, and Photoluminescence spectroscopies were used to analyse all the samples. XRD technique was used for structural examination of Ba_0.6Sr_0.4-xYb_xFe_12-yCo_yO₁₉. The XRD patterns of Yb–Co co-substituted M-type hexaferrites revealed the pure single phase of synthesized samples. Change in Yb–Co concentration influenced lattice parameters and unit cell volume. The variations in lattice constants "a" and "c" values are 5.891–5.862 and 23.180–23.317. FTIR spectroscopic data graphs revealed the formation of several absorption bands from 430 cm^?1 to 3000 cm^?1. The strain in the unit cell produced by substitution changes in Raman spectra which is also confirmed by XRD. Many 630 nm–700 nm emissions were observed in the PL spectra of Ba_0.6Sr_0.4-xYb_xFe_12-yCo_yO_19. Furthermore, a bandgap of 1.961–1.875 eV was observed for the pure sample. The substitution improves the dielectric losses and Ac conductivity. The Maxwell-Wagner theory was used to investigate the changing trends of characteristics regarding dielectric parameters. The findings show that the samples with the appropriate cationic substitution can be used in microwave and high-frequency applications.     

Enhanced microwave absorption features of Ba3Co2Fe24O41 hexaferrite by high lanthanium doping concentration

Controlling material structure and its electromagnetic properties, including complex permittivity and permeability, could enhance the microwave absorption performance of the material in terms of reflection loss and effective absorption bandwidth. In this study, La-substituted barium hexaferrite, Ba_3−xLa_xCo₂Fe₂₄O₄₁ (x = 0, 0.1, 0.3, and 0.5) compounds were successfully prepared using the solid-state reaction method, and their corresponding microstructures, static magnetic properties, and electromagnetic features in 2–18 GHz were investigated. The doping of La content increased saturation magnetization, coercivity, and remnant magnetization. The Ba_2.7La_0.3Co₂Fe₂₄O₄₁ epoxied sample with 3.5 mm thickness possessed an excellent microwave absorption of −47.3 dB at 3.52 GHz, and its corresponding effective absorption bandwidths were 3.75 GHz (2.25–6 GHz) and 0.57 GHz (17.43–18 GHz). It is shown that doping with various La concentrations on Ba₃Co₂Fe₂₄O₄₁ can be used as an effective technique to tune the performance of microwave absorbers based on barium hexaferrite.     

Effect of strontium substitution on the structure and dielectric properties of unfilled tungsten bronze Ba4-xSrxSmFe0.5Nb9.5O30 ceramics

The effects of Sr²⁺ substitution for Ba²⁺ on phase structure, microstructure, dielectric and electric properties for Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ (x = 0, 1, 2, 3 and 4) ceramics were systematically researched. X-ray diffraction patterns show that Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ (x = 0, 1, 2 and 3) ceramics are tetragonal tungsten bronze compound with a space group of P4bm, while the sample for x = 4 is an orthorhombic structure compound. The result can be corroborated by the analysis of Raman spectroscopy. As the Sr²⁺ contents increase from 0 to 3, the full width at half maximum of Raman lines of all samples increase gradually, indicating that the degree of lattice distortion increase. All tetragonal tungsten bronze ceramics exhibited a broad permittivity peaks, accompanied by frequency dispersion, indicating all samples are relaxor. The electrical properties of BSSFN ceramics were further studied by complex impedance spectroscopy. XPS spectrum shows that Fe²⁺ and Fe³⁺ coexist in Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ ceramics, and their proportion varies with the concentration of Sr²⁺.     

Preparation,X-ray phase analysis and dielectric properties of Pb(Fe1-xCox)2/3W1/3O3 and Pb(Co1-yFey)1/2W1/2O3 (0 ≤ x,y ≤ 1) systems

In this work, the Pb(Fe_1-xCo_x)_2/3W_1/3O₃ (PFCW) and Pb(Co_1-yFe_y)_1/2W_1/2O₃ (PCFW) ceramics with 0 ≤ x, y ≤ 1 were successfully fabricated by a solid-state reaction process. X–ray diffraction phase analysis indicate the formation of two different series of solid solutions with a perovskite structure and with the substitution limits of Fe for Co (in PFCW) and Co for Fe (in PCFW) are x = 0.35 and y ≈ 0.05, respectively. Based on the results of dielectric study of the PFCW ceramics, it was shown that a crossover from relaxor ferroelectric to ferroelectric with a diffuse phase transition takes place at x = 0.10. In the case of PCFW ceramics, the observed dielectric maxima correspond to the phase transitions at 320 K and 256 K. The peculiarities of the temperature dependencies of the thermally stimulated depolarization currents of PFCW and PCFW solid solutions were studied and discussed.     

Influence of rare-earth La3+ ion doping on microstructural,magnetic and dielectric properties of Mg0.5Ni0.5Fe2-xLaxO4 (0 ≤ x ≤ 0.1) ferrite nanoparticles

A series of La³⁺ ion doped magnesium nickel ferrites, Mg_0.5Ni_0.5Fe_2-xLa_xO₄ (0 ≤ x ≤ 0.1) having a cubic spinel structure were prepared by the co-precipitation method. Various characterization techniques, including X-ray diffractometer (XRD), high resolution transmission electron microscopy (HR-TEM), electron spin resonance (ESR) and vibrating sample magnetometer (VSM) were used to investigate structural and magnetic properties. The average crystallite size decreases and lattice parameter increases with La³⁺ ion doping and lie in the range of 12–7 nm and 8.347–8.361 Å respectively. Analysis of ESR spectra reveals that, g-value with La³⁺ ion addition decreases from 2.57 to 2.12. The saturation magnetization and the coercivity decrease with increasing rare-earth content. Magnetic-hysteresis (M − H) loop shifts from a ferromagnetic to a superparamagnetic nature with La³⁺ ion addition. The dielectric study was carried out in the frequency range of 1 KHz to 4000 KHz and temperature ranging 30 °C–350 °C using the impedance analyzer. The dielectric constant decreases with increasing frequency and the La³⁺ ion concentration. The dielectric loss of the sample increases with increasing temperature. The magnetic properties of the synthesized nanoparticles make them a potential material for stable ferrofluid application and the low tangent loss value makes these material a potential candidate for frequency-based applications.     

Ferroelectric,dielectric, magnetic,structural and photocatalytic properties of Co and Fe doped LaCrO3 perovskite synthesized via micro-emulsion route

In the present investigation, La_1-xCo_xCr_1-yFe_yO₃ (x,y = 0.0, 0.12, 0.36, 0.60) perovskite was fabricated via a facile micro-emulsion route. The synthesized perovskites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques to examine the effect of Co and Fe ions on the physico-chemical properties. The ferroelectric, dielectric, and magnetic properties of La_1-xCo_xCr_1-yFe_yO₃ were changed significantly as a function of dopants contents (Co and Fe ions). Outcomes revealed that the dielectric, ferroelectric and magnetic properties of LaCrO₃ perovskite can be tuned significantly via Co and Fe doping and La_0.40Co_0.60Cr_0.40Fe_0.60O₃ have potential for photocatalytic dye removal under (visible) light expoure. The photocatalytic activity (PCA) of the pristine LaCrO₃ and La_0.40Co_0.60Cr_0.40Fe_0.60O₃ photocatalyst was evaluated under (visible) light irradiation for crystal violet (CV) dye. Experimental results revealed that La_0.40Co_0.60Cr_0.40Fe_0.60O₃ photocatalyst degrdae almost 77.21% CV dye with the rate constant value of 0.01475 min^?1. In the presence of isopropyl alcohol (IPA) scavenger, the PCA of the La_0.40Co_0.60Cr_0.40Fe_0.60O₃ photocatalyst and rate constant value of the photocatalytic reaction decreased to 32.5% and 0.00491 min^?1, suggesting the superoxide as main active specie. Results revealed that Co and Fe doping doped material is efficient for photocatalytic presentations under solar light expoure.     

Structural,optical, electrical,dielectric, molecular vibrational and magnetic properties of La3+ doped Mg–Cd–Cu ferrites prepared by Co-precipitation technique

Ferrites are among the most frequently investigated materials mainly due to interesting and practically different properties. Therefore, easily and cost-effective lanthanum doped Mg_0.5Cd_0.25Cu_0.25Fe_2-xLa_xO₄ (x = 0.0, 0.0125, 0.025, 0.0375 and 0.05) ferrites were synthesized by a co-precipitation route, a comprehensive characterisation of their structural, optical, electric, dielectric, molecular vibrational, and magnetic properties were carried out. X-ray diffraction analysis confirmed the formation of a cubic spinel structure. Variations in frequency bands were also observed with amplification in optical band gap energy (2.95 – 3.38 eV) due to La³⁺ ions insertion. The electric resistivity had opposite trends at low and high temperatures with increasing La³⁺ content. The Curie temperature, activation energy, and drift mobility were also determined to have values consistent with the semiconducting behavior of the soft ferrites. The saturation magnetization (M_S) has a maximum value 49.385 emu/g with remanent magnetization (M_r) was 34.928 emu/g and coercivity 661.4 Oe for La³⁺ concentration x = 0.05. The minimum dielectric loss was observed for La³⁺ concentration x = 0.025. Moreover, the resistivity (ρ) has a maximum value of 7.95 × 10⁴ Ω cm for La³⁺ concentration x = 0.025. The calculated frequency range of La³⁺ doped Mg–Cd–Cu ferrites was detected in the microwave range (3.36 – 10.80 GHz), suggesting the potential application of the materials in longitudinal recording media and microwave absorbance.     

The role of Pb and annealing temperature on the structural,magnetic, optical and dielectric properties of W-type hexaferrite nanostructures

In this paper, W-type Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructures were synthesized by auto-combustion sol-gel method. Then, the effects of annealing temperature and Pb contents on the structural, magnetic, optical, and dielectric properties of Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructure were investigated. First, a gel of metal nitrates with a specific molar ratio with x different was prepared and then the gel was annealed at different temperatures for 4?h. To determine the annealing temperature of the samples, the prepared gel was examined by thermogravimetric analysis and differential thermal analysis. The morphology and crystal structure of the prepared samples were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction pattern (XRD). The results of XRD patterns indicated that the annealing temperature of synthesized Sr_1-xPb_xCo₂Fe₁₆O₂₇ was reduced by increasing Pb contents. In addition, FESEM images showed that the microstructure of the samples was homogeneous and uniform, but since the samples have a magnetic property, the particles were aggregated. Fourier transform infrared analysis (FT-IR) was used to confirm the phase formation. The FT-IR results of the samples indicated that the tetrahedral and octahedral sites, which are the important attributes of hexaferrites, were formed. The magnetic properties of the samples were measured by vibrating sample magnetometer (VSM). The VSM results of the samples showed that because of increasing Pb content, the amount of saturation magnetization and that of magnetic coercivity decreased from 81.29 to 10.23?emu/g and 2285–477?Oe, respectively. The optical properties of the samples were investigated by ultraviolet–visible spectroscopy, which revealed that the energy gap decreases and the absorption peaks move towards longer wavelengths by increasing Pb content. The dielectric properties of the samples were investigated by the LCR meter. It was found that by increasing frequency, the dielectric constant (ε^′) and the dielectric loss (?) of the samples were decreased.     

Effect of dopant on ferroelectric,dielectric and photocatalytic properties of Co–La-doped dysprosium chromite prepared via microemulsion route

In the current study, pristine and a series of La and Co-doped dysprosium chromite (Dy_1-yLa_yCr_1-xCo_xO₃) nanoparticles have been fabricated via a facile microemulsion technique. The influence of doping was evaluated based on structural, ferroelectric, dielectric, and photocatalytic properties. The prepared nanoparticles were characterized by XRD, SEM, Raman, and UV–Vis techniques. XRD patterns confirm the synthesis of a monophase orthorhombic structure with space group Pbnm with an average crystalline size in the 18–37 nm range. The saturation polarization (Ps), remanence (Pr), and coercivity (Hc) were determined using a hysteresis loop, and it was observed that by increasing the concentration of dopants, the value of Ps and Pr were improved. According to the PL spectra, highly substituted materials had a low recombination rate and higher charge separation (e^? - h⁺), which was ultimately accountable for higher photocatalytic activity. The dielectric loss decreases with frequency and dopant concentration. The photocatalytic activity of Dy_1-yLa_yCr_1-xCo_xO₃ was investigated against Crystal Violet (CV) dye under sunlight irradiation. The Dy_1-yLa_yCr_1-xCo_xO₃ furnished a 70% dye degradation in 90 min, which is attributed to the tunned bandgap and efficient electron-hole pair separation and the photocatalytic activity under visible light making Dy_1-yLa_yCr_1-xCo_xO₃ a promising photocatalyst for dye removal from wastewater.     

Dielectric and magnetic properties of (Pb,Ti) co-doped BiFeO3 multiferroic ceramics

In this study, Bi_0.9Pb_0.1Fe_1-xTi_xO₃ (0.05 ≤ x ≤ 0.20) multiferroic ceramics were prepared through solid-state reaction. The influence of Pb, Ti partial substitutions on the dielectric and magnetic properties of BiFeO₃ multiferroic ceramics was investigated and discussed in detail. X-ray diffractions confirm rhombohedral perovskite phase formation (R3c space group). Scanning electron microscopy (SEM) was employed to investigate the morphology, revealing a cuboidal microstructure with bimodal distribution of grain sizes. Magnetic studies were carried out and the results reveal a slight enhancement of saturation magnetization with Ti concentration increasing. The present data indicates that Bi_0.9Pb_0.1Fe_1-xTi_xO₃ can be used as multifunctional material in different magnetoelectric applications.     

Effect of Mg doping on magnetic,and dielectric properties of NiCr2O4 nanoparticles

The structural, magnetic, and dielectric properties of spinel Magnesium (Mg) doped Nickel chromite (NiCr₂O₄) nanoparticles (NPs) have been studied in detail. The X-ray powder diffraction exhibited normal spinel phase formation of Mg_xNi_1-xCr₂O₄ (x = 0, 0.2, 0.4, 0.6, and 1) NPs with a maximum average crystallite size of about 44 nm for x = 0.2 composition. The FTIR spectra of these NPs revealed the characteristic Ni–O and Mg–O and Cr–O bands around 639 cm^?1 and 497 cm^?1, respectively which confirmed the spinel structure. Temperature-dependent zero field cooled and field cooled graphs of NiCr₂O₄ NPs showed phase changes from ferrimagnetic to paramagnetic state at 86 K, while MgCr₂O₄ NPs showed antiferromagnetic (AFM) transition at Neel temperature (T_N) at 15 K due to corner-sharing of Cr³⁺ ions at a tetrahedral lattice site resulting in a highly magnetic frustrated structure. The field dependent magnetization (M ? H) loops of Mg_xNi_1-xCr₂O₄ NPs confirmed the competing AFM interactions and ferrimagnetic interactions resulting in a sharp decreased saturation magnetization with Mg doping. Dielectric constant, dielectric loss, and ac conductivity of these NPs showed size-dependent variation and depicted maximum value at x = 0.2 Mg concentration. In summary, the magnetic and dielectric properties of Mg doped NiCr₂O₄ NPs were modified by variations in the average crystallite size and magnetic exchange interactions, which may be suitable for different technological applications.     

Low-temperature firing and microwave dielectric properties of MgNb2-xVx/2O6-1.25x ceramics

MgNb_2-xV_x/2O_6-1.25x (0.1≤x≤0.6) ceramics with orthorhombic columbite structures were prepared at low-temperature by a solid-phase process. The phase component, microscopic morphology, low-temperature sintering mechanism and microwave dielectric performance of MgNb_2-xV_x/2O_6-1.25x ceramics were comprehensively investigated. Low-temperature sintering densification of dielectric ceramics was achieved via the nonstoichiometric substitution of vanadium (V) at the Nb-site. In contrast to pure MgNb₂O₆ ceramics, the sintering temperature of MgNb_2-xV_x/2O_6-1.25x (x = 0.2) ceramics was reduced by nearly 300 °C owing to the liquid-phase assisted sintering mechanism. The liquid phase arises from the autogenous low-melting-point phase. Meanwhile, MgNb_2-xV_x/2O_6-1.25x (x = 0.2) samples with nonstoichiometric substitution could achieve a more than 900% improvement in the Q × f value, compared with stoichiometrically MgNb_2-xV_xO₆ (x = 0.1, 0.2) ceramics. Finally, MgNb_2-xV_x/2O_6-1.25x dielectric ceramics possess outstanding microwave dielectric properties: ε_r = 20.5, Q × f = 91000, and τ_f = -65 ppm/°C when sintered at 1030 °C for x = 0.2, which provides an alternative material for LTCC technology and an effective approach for low-temperature sintering of Nb-based microwave dielectric ceramics.     

Synthesis and magnetic properties of La3+-Co2+ substituted strontium ferrite particles using modified spray pyrolysis–calcination method

The purpose of the research was to improve the intrinsic magnetic properties of strontium ferrite by substituting lanthanum and cobalt for strontium and iron. The salt-assisted ultrasonic spray pyrolysis (SA-USP) following calcination process were used to from La-Co substituted strontium ferrite particles (La_xSr_1-xFe_12-yCo_yO₁₉), and their compositional dependent magnetic properties systemically investigated. All the samples were calcined at 1050 °C for 1 h in an air atmosphere to yield single-phased hexagonal particles several hundred nanometers to microns in size. A saturation magnetization of 70.76 emu/g and a coercivity 7265 Oe were obtained at a composition of La_0.25Sr_0.75Fe_11.75Co_0.25O₁₉. The amount of Co was reduced to obtain an optimized saturation magnetization of 71.40 emu/g and a coercivity of 7572 Oe at a composition of La_0.25Sr_0.75Fe_11.8Co_0.2O₁₉.     

Suppression of Sr surface segregation in La0.8Sr0.2Co0.2Fe0.8O3-δ via Nb doping in B-site

Sr surface segregation has been one of the main reasons for the cathode performance degradation during the long-term operation of solid oxide fuel cells (SOFC). Investigation on Sr segregation mechanism and proposing strategies on suppressing the Sr surface segregation are significant for SOFC development. In this paper, La_0.8Sr_0.2Co_0.2Fe_0.8-xNb_xO_3-δ (LSCFNb, x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) are prepared via sol-gel method. The electrochemical performance and long-term stability are tested through electrochemical impedance spectroscopy (EIS) and constant current polarization. The results show that the long-term stability of LSCFNb cathodes are strongly affected by Nb content. Combining the results of ICP and XPS, it's revealed that the Sr surface segregation can be effectively suppressed with the increase of Nb content. The LSCFNb cathodes gain the optimal electrochemical performance when x = 0.04, with minimum polarization resistance of 0.27 Ω cm² at 750 °C and oxygen reduction reaction activation energy of 1.54 eV. After cathodic polarization for 144 h, the polarization resistance and activation energy of LSCFNb4 cathode increase slightly, revealing it a promising cathode material for SOFC research.     

Multiple magnetic phase transitions in NixMn1-xCo2O4

We prepared pure-phase Ni_xMn_1-xCo₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni_xMn_1-xCo₂O₄ increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni_0.5Mn_0.5Co₂O₄ sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni_xMn_1-xCo₂O₄ (x = 0 and 0.25), and as the concentration of Ni increases, Ni_xMn_1-xCo₂O₄ (x = 0.75 and 1) show a spin glass state. The structure of Ni_xMn_1-xCo₂O₄ (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni_xMn_1-xCo₂O₄ and that the strength of the Ni-O bond is greater than that of the Mn-O bond.     

A medium-entropy perovskite oxide La0.7Sr0.3Co0.25Fe0.25Ni0.25Mn0.25O3-δ as intermediate temperature solid oxide fuel cells cathode material

In this study, we report a novel medium-entropy perovskite oxide of La_0.7Sr_0.3Co_0.25Fe_0.25Ni_0.25Mn_0.25O_3-δ (LSCFNM73) with high constitutive entropy (S_config) as the cathode material of intermediate temperature solid oxide fuel cells (IT-SOFCs). The intrinsic properties of phase structure, electrical conductivity, thermal expansion and oxygen adsorption capacity of La_1-xSr_xCo_0.25Fe_0.25Ni_0.25Mn_0.25O_3-δ (LSCFNM, x = 0, 0.1, 0.2, 0.3) oxides are evaluated in detail. The LSCFNM73 oxide exhibits the maximum electrical conductivity of 464 S cm⁻¹ at 800 °C and a relatively lower thermal expansion coefficient (TEC) of 15.34 × 10⁻⁶ K⁻¹, which is selected as the propriate cathode composition. The B-site of LSCFNM73 contains four elements which can increase the configuration entropy. Additionally, NiO-Yttria stabilized zirconia (YSZ) supported fuel cell is fabricated by tape casting, hot pressing-lamination, co-sintering and screen printing technologies. The fuel cell demonstrates a maximum power density of 1088 mW cm² at 800 °C, and excellent stability at 750 °C under 0.75V in 120 h and 10 times thermal cycling between 750 °C and 400 °C. Therefore, the medium-entropy LSCFNM73 oxide can be applied in IT-SOFCs as a competitive cathode material.     

Variable optical properties of La0.5Sr0.5Co1-xNixO3-δ for high-temperature resistant code application

La_0.5Sr_0.5Co_1-xNi_xO_3-δ (x = 0, 0.1, 0.3, 0.5) ceramics were prepared via tape casting and solid state reaction process. The influence of Ni concentration on the optical properties of La_0.5Sr_0.5Co_1-xNi_xO_3-δ has been investigated. Results showed that the reflectance in the range of 0.3–15 μm decreased with the increment of Ni concentration, thereby causing a change in the color phase parameters and emissivity. Based on the difference in L* values and emissivity, the letters (HOT) and QR codes (NJTECH) were fabricated. The developed letters and QR codes could be identified both at room and high temperatures. Furthermore, the QR codes were read out successfully even underwent heat treatment at 1000 °C. The results in this work demonstrate a new application of La_0.5Sr_0.5Co_1-xNi_xO_3-δ ceramics.