Critical influence of different diamagnetic ions on electromagnetic properties of BaFe12O19

The correlation between the electromagnetic properties of BaFe_12-xD_xO₁₉ (0.1?x?1.2) solid solutions (D = Al³⁺, In³⁺ and Ga³⁺) and the concentration of diamagnetic ions was investigated. The changes of electromagnetic properties of the investigated samples were explained using neutron powder diffraction and Mossbauer spectroscopy data. The diamagnetic ions with different ionic radii and electronic configurations were chosen. The transmission spectra of all the samples demonstrated a deep minimum in the frequency range 20–65?GHz which was associated with the natural ferromagnetic resonance. The resonance frequency $f_{\mathit{res}}$ and amplitude were changed by the substitution type and level. With increasing the substitution concentration, the resonance frequency increases from 51?GHz to 61?GHz and decreases from 50.5?GHz to 27?GHz for Al- and In-substituted samples, respectively. More complicated concentration dependences of resonance characteristics were obtained for Ga-substituted samples in a narrow range of 49–50.5?GHz. The value of $f_{\mathit{res}}$ had a minimum around x?=?0.6 and further increased to 50.5?GHz for x?=?1.2. It was concluded that the intrasublattice interactions were responsible for tailoring the magneto crystalline anisotropy and resonance parameters. More detailed investigations would require the development of phenomenological model on the basis of the electronic structure using Goodenough-Kanamori approaches.     

LiCa3MgV3O12:Sm3+: A new high-efficiency white-emitting phosphor

A novel single-phased white-light-emitting phosphor Sm³⁺ doped LiCa₃MgV₃O₁₂ (LCMV) was developed. The LCMV host was one self-activated bluish-green emitting phosphor, which possessed an efficient excitation band in the 250–400?nm wavelength range and showed an intense broadband bluish-green emission with internal quantum efficiency (IQE) of 39%. Doping Sm³⁺ ions in to LCMV host induced tunable-color emissions, due to the energy transfer from [VO₄]^3? to Sm³⁺ ions. Importantly, under 340?nm excitation, the LCMV:Sm³⁺ can emitted bright white light by combining the self-activated luminescence of LCMV host and the red emissions of Sm³⁺ ions, and the IQE of the white-emitting composition-optimized LCMV:0.01Sm³⁺ phosphors reached up to 45%. These white-emitting LCMV:Sm³⁺ phosphors have potential applications in white light-emitting diodes and optical display devices.     

Structural and spectroscopic properties of Yb3+ doped borophosphate glasses for IR laser application

Ytterbium (Yb³⁺) doped borophosphate (BPYb) glasses have been prepared and studied by means of their physical, optical, structural and spectroscopic properties aiming laser performance parameters. The main structural groups, ${\mathrm{PO}}_3^{2?}$, ${\mathrm{P}}_2{\mathrm{O}}_7^{4?}$ and BO₄ of the borophosphates were analyzed through their FTIR-ATR and Raman spectra. A linear increment of the absorption coefficient and of the integrated emission intensity were observed with increase of Yb³⁺ ions. The absorption and emission cross-sections have been evaluated and reported. Decay lifetimes were found to decrease with the increase of Yb³⁺ ions. The evaluated laser performance parameters (I_sat and I_min), figure of merit and cross-sections (absorption and emission) suggest that 0.5?mol% of Yb³⁺ doped borophosphate glass is the most appropriate candidate for solid state infrared (IR) laser applications.     

Gd3+ doping induced enhanced upconversion luminescence in Er3+/Yb3+ co-doped transparent oxyfluoride glass ceramics containing NaYF4 nanocrystals

In this article, transparent oxyfluoride glass ceramics containing $\mathrm{\beta }$-NaYF₄ nanocrystals were successfully prepared via Gd³⁺ doping. Compared to conventional non-doped glasses, the thermal treatment temperature required for the precipitation of $\mathrm{\beta }$-NaYF₄ nanocrystals can be lowered with the doping of Gd³⁺. Furthermore, under the same thermal treatment condition, more $\mathrm{\beta }$-NaYF₄ nanocrystals were precipitated in Gd³⁺ doped ones, which greatly improves the luminescence efficiency of rare earth doped glass ceramics. Possible mechanism for the Gd³⁺ doping induced enhanced upconversion luminescence phenomenon was proposed, based on thorough structural and optical characterizations. The results revealed that the doping of Gd³⁺ ions could decrease the crystallization activation energy and promote the formation of Y-F-Na bonding, which helps the precipitation of $\mathrm{\beta }$-NaYF₄ nanocrystals. Consequently, a large enhancement in upconversion luminescence was achieved. Moreover, the strategy can be successfully applied to the development of other glass ceramic systems for various optoelectronic applications.     

Magnetic and magnetotransport properties of La1−xSrxMn0.5Сo0.5O3 perovskites

La_1?xSr_xMn_0.5Сo_0.5O₃ (x ≤ 0.75) perovskites have been studied as a function of temperature by neutron powder diffraction (NPD), magnetization and magnetoresistance measurements. The NPD data show that x = 0.15 and 0.5 compounds are stoichiometric, so the Sr²⁺ doping transforms Co²⁺ ions into the Co³⁺ ones, whereas manganese ions remain in the 4+ oxidation state as in the parent ferromagnetic compound ${\mathrm{LaCo}}_{\mathrm{0.5}}^{\mathrm{2}+}{\mathrm{Mn}}_{\mathrm{0.5}}^{\mathrm{4}+}{\mathrm{O}}_{\mathrm{3}}$. The magnetization data show a decrease in the Curie temperature from 215 K for the compound with x = 0 down to 147 K for the compound with x = 0.05. The compounds with x > 0.15 show an increase in T_C up to 260 K (x = 0.75) in spite of a gradual decrease of the spontaneous magnetization. The stoichiometric compound x = 0.5 demonstrates a sharp ferromagnet-paramagnet transition with T_C = 250 K. However, there is no visible coherent magnetic contribution to the NPD patterns. All compounds are semiconductors and exhibit large magnetoresistance gradually increasing with decrease of temperature. The magnetic data have been interpreted assuming that the Co³⁺ ions are in high spin state, however, there is a fraction of cobalt ions in low spin state. It is suggested that the superexchange interaction between Co³⁺ ions in the high spin state and Mn⁴⁺ ions is ferromagnetic and that the ferromagnetism of the compounds with x > 0.5 and high T_C is associated with positive exchange interactions between Co³⁺ being in high spin state and Mn⁴⁺ ions distributed within the short range regions. Based on the NPD results and magnetization data the magnetic phase diagram has been constructed.     

Effect of oriented defect-dipoles on the ferroelectric and piezoelectric properties of CuO-doped (K0.48Na0.52)0.96Li0.04Nb0.805Ta0.075Sb0.12O3 ceramics

The orientation characteristics of the defect dipoles formed by acceptor ions (${\mathrm{Cu}}_{\mathrm{Nb}}^{″\prime }$) and oxygen vacancies ($V_{\mathrm{O}}^{??}$) in CuO-doped (K_0.48Na_0.52)_0.96Li_0.04Nb_0.805Ta_0.075Sb_0.12O₃ piezoceramics were investigated. The ferroelectric and piezoelectric properties of the ceramics were obviously affected by the defect dipoles which are oriented along with the domains when poled under a dc electrical field of 3.5?kV/mm at the temperature near T_C. The poled ceramics with 1.0–3.0?mol% CuO displayed strong asymmetric P-E loops and a large internal bias field (E_i), 3.89–4.57?kV/cm, when polarized at the temperature near T_C. The enhanced piezoelectric coefficient d₃₃, 186–192?pC/N, was obtained for the ceramics poled near T_C when 0.02?≤?x?≤?0.03. The ceramics with oriented defect dipoles showed a relatively good thermal stability of d₃₃ until 180?°C.     

Effect of Ti3AlC2 precursor on the electrochemical properties of the resulting MXene Ti3C2 for Li-ion batteries

The presented work compared the etching behavior between combustion synthesized Ti₃AlC₂ (SHS-Ti₃AlC₂) and pressureless synthesized Ti₃AlC₂ (PLS-Ti₃AlC₂). Because the former had a more compact structure, it was harder to be etched than PLS-Ti₃AlC₂ under the same conditions. When served as anode material for Li-ion batteries, SHS-Ti₃C₂ showed much lower capacity than PLS-Ti₃C₂ at 1?C (52.7 and 87.4?mAh?g^?1, respectively) due to the smaller d-spacing. Furthermore, Potentiostatic Intermittent Titration Technique (PITT) was used to determine the Li-ion chemical diffusion coefficient (${\mathrm{D}}_{{\mathrm{Li}}^{+}}$) of Ti₃C₂ in the range of 10^?10 ??10^?9 cm² s^?1, indicating that Ti₃C₂ could exhibit an excellent diffusion mobility for Li-ion.     

Giant negative electrocaloric effect and energy storage response in 0.94(K0.5Na0.5)NbO3-0.06SrMnO3 nanocrystalline ceramics

We report the electrocaloric (EC) effect investigation on lead-free 0.94(K_0.5Na_0.5)NbO₃-0.06SrMnO₃ nanocrystalline ceramics by an indirect thermodynamic method using Maxwell's relations. The maximum value of the negative EC effect ($\mathrm{\Delta }{\mathrm{T}}_{\mathit{max}}=?1.66\mathrm{K}$) was observed at 459?K near the transition temperature at the field of 50?kV/cm. The corresponding EC responsivity was calculated to be $?3.32\times {10}^{?7}\mathrm{K}\mathrm{m}/\mathrm{V}$ under 50?kV/cm at 459?K whereas the coefficient of performance (COP) and recoverable energy density (${\mathrm{W}}_{\mathit{rec}}$) were found to be 1.03 and $0.17\mathrm{J}/{\mathrm{cm}}^3$, respectively under 50?kV/cm at 443?K. The observed values of negative EC effect, and EC responsivity are larger than any other lead-free ferroelectric ceramics with good COP and ${\mathrm{W}}_{\mathit{rec}}$ value. The results are interesting to improve the cooling efficiency and energy storage for device application.     

Synthesis of coral-shaped yttrium-aluminium-iron garnets by solution-combustion method

Aluminium substituted yttrium-iron garnet (Y₃Al_xFe_5?xO₁₂, x = 0, 1, 2, 3, 4 and 5) powders were synthesized by solution combustion route followed by calcination at 1000 °C for 6 h. According to the X-ray diffraction (XRD) results, the as-prepared samples were amorphous. Calcination of the samples at 1000 °C for 6 h results in the formation of phase pure (Ia$\stackrel{?}{\mathit{3}}$d) garnet structure. The morphology of the samples (for all compositions) were found to be coral-network-like. The Rietveld refinement of the XRD patterns and the Mössbauer spectroscopy confirmed that Y³⁺ ions occupy the dodecahedral site, whereas Al³⁺ and Fe³⁺ ions are distributed in the tetrahedral and octahedral sites of the bcc (Ia$\stackrel{?}{\mathit{3}}$d) structure of the garnet phase. The Al³⁺ ions have a preference to occupy the octahedral site. The lattice parameter decreases with increase in Al-content due to the small size of the Al³⁺ cations. For the yttrium-iron-garnet (YIG) sample (x = 0), a saturation magnetization (M_S) value of ~ 29 emu/g was obtained, which decreases to ~ 7 emu/g for the sample with x = 2. Further addition of Al makes the garnets paramagnetic. The coral network shape of our garnet samples renders them useful for various applications in catalysis.     

Theoretical analysis and synthesis of Al4O4C and Al2CO phase in the resin bonded Al-Al2O3 refractory in N2-flowing

In flowing nitrogen, Al₄O₄C and Al₂CO bonded Al₂O₃-based composite was successfully prepared by a gaseous phase mass transfer pathway at 1600 °C for 3 h after an Al-AlN core-shell structure was formed in the resin bonded Al-Al₂O₃ refractory at 580 °C for 8 h. The formation mechanism of Al₄O₄C and Al₂CO phase is as follows. An Al-AlN core–shell structure is built at 580 °C for 8 h and broken at higher temperatures, and then, Al(g) reacts with C from the resin and N₂ to form Al₄C₃ and AlN, respectively. Owing to the exothermic reaction of the Al₄C₃ and AlN formation, the reaction temperature in the resin bonded Al-Al₂O₃ refractory is above the practical environmental temperature; for instance, the reaction temperature is above 1715 °C at 1600 °C in this work. Therefore, Al₄C₃ reacts with Al₂O₃ to generate Al₄O₄C and then Al₄O₄C is transformed into Al₂OC by the reaction ${\mathrm{Al}}_4{\mathrm{O}}_{\mathrm{4}}{C(s)+\text{Al}}_4{\mathrm{C}}_{\mathrm{3}}(s)\to {\mathrm{4Al}}_{\mathrm{2}}\text{OC}(s)$ at elevated temperatures. Al₂OC solid solution is finally formed through the dissolution of AlN into Al₂OC.     

Photoluminescence and optical temperature sensing in Sm3+-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

A series of orange-red emitting Sm³⁺ activated Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCZT: xSm³⁺, x?=?0.001–0.007) are synthesized by a conventional solid-state reaction method. The Sm³⁺ ions composition dependent photoluminescence properties are systematically investigated. Under the excitation of a 407?nm near-ultraviolet light, the ceramics exhibit strong characteristic emission of Sm³⁺ ions with dominant orange-red emission peak at around 595?nm, which is ascribed to the transition of ⁴G_5/2 → ⁶H_7/2. The BCZT: 0.004Sm³⁺ ceramic displays the optimal emission among these Sm³⁺-doped BCZT solid solutions. Moreover, the photoluminescence intensity exhibits extremely sensitive to temperature, suggesting that BCZT: 0.004Sm³⁺ could be applicable for temperature sensing. A maximum relative sensitivity of 1.89%?K^?1 at 453?K is obtained. Furthermore, the existence of ferroelectricity in the BCZT host combined with Sm³⁺ activated photoluminescence properties could be useful for developing optical-electro multifunctional materials and devices.