Structure and cation distribution in perovskites with small cations at the A site: the case of ScCoO3

Abstract

We synthesize ScCoO₃ perovskite and its solid solutions, ScCo_1?xFe_xO₃ and ScCo_1?xCr_xO₃, under high pressure (6 GPa) and high temperature (1570 K) conditions. We find noticeable shifts from the stoichiometric compositions, expressed as (Sc_1?xM_x)MO₃ with x = 0.05–0.11 and M = Co, (Co, Fe) and (Co, Cr). The crystal structure of (Sc_0.95Co_0.05)CoO₃ is refined using synchrotron x-ray powder diffraction data: space group Pnma (No. 62), Z = 4 and lattice parameters a = 5.26766(1) Å, b = 7.14027(2) Å and c = 4.92231(1) Å. (Sc_0.95Co_0.05)CoO₃ crystallizes in the GdFeO₃-type structure similar to other members of the perovskite cobaltite family, ACoO₃ (A³⁺ = Y and Pr-Lu). There is evidence that (Sc_0.95Co_0.05)CoO₃ has non-magnetic low-spin Co³⁺ ions at the B site and paramagnetic high-spin Co³⁺ ions at the A site. In the iron-doped samples (Sc_1?xM_x)MO₃ with M = (Co, Fe), Fe³⁺ ions have a strong preference to occupy the A site of such perovskites at small doping levels.     

Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3

The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr_1.261CoO₃ has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr_1.261CoO₃ is a composite crystal that consists of the [CoO₃] and [2Sr] subsystems. The [CoO₃] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO₆ polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO₃] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co–O bonds than the Oh sites: d_av. =2.039(4) Å (TP) and 1.895(3) Å (Oh). The averaged Co bond valences are Co^3.56(3)+ in the Oh sites and Co^2.45(3)+ in the TP sites, suggesting that a considerable amount of Co³⁺ ions are mixed with Co⁴⁺ions in the Oh sites and with Co²⁺ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S=0 low-spin state for Co³⁺(dε⁶), S=1/2 low-spin state for Co⁴⁺(dε⁵) and S=3/2 high-spin state for Co²⁺(dε⁵dγ²). The Weiss temperature, approximately 0.8 K, implies that Sr_1.261CoO₃ naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co³⁺ ions. These results suggest that the nonmagnetic Co³⁺ ions play an essential role in the magnetism of Sr_2γCoO₃ systems.     

High-temperature resistivity and thermoelectric properties of coupled substituted Ca3Co2O6

Polycrystalline samples of Ca_3−xNa_xCo_2−xMn_xO₆ (x=0.0–0.5) have been prepared by the sol-gel cum combustion method using sucrose in order to investigate the effects of the coupled substitution of Na and Mn on Ca and Co sites on the transport properties of Ca₃Co₂O₆(Co326). The products were characterized by Fourier transform infrared spectroscopy, powder x-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis and scanning electron microscopy. XRD patterns reveal the formation of single-phase products up to x=0.5. Coupled substitution increases the solubility of both Na and Mn on Ca and Co sites, respectively, in contrast to the limited solubility of Na and Mn (x=0.2) when separately substituted. TGA confirms the formation of the Ca₃Co₂O₆ phase at temperatures ∼720 °C. The grain size of the parent and substituted products is in the range 150–250 nm. Electrical resistivity and Seebeck coefficient were measured in the temperature range 300–800 K. Resistivity shows semiconducting behavior for all the compositions, particularly in the low-temperature regime. The Seebeck coefficient increases with temperature throughout the measured temperature range for all compositions. The maximum Seebeck coefficient (200 μV K⁻¹) is observed for x=0.5 at 825 K, and this composition may be optimal for high-temperature thermoelectric applications.     

Magnetic susceptibility, spin transition, and electrical conductivity of LaCo1 + xO3 and NdCo1 + xO3

The magnetic susceptibility of Nd₂O₃, NdCo_{1 + x} O₃, and LaCo_{1 + x} O₃ (x = 0, 0.05, 0.1, 0.15) has been measured at temperatures from 80 to 950 K, and the electrical conductivity of the neodymium and lanthanum cobaltites (enriched in cobalt relative to neodymium or lanthanum) with the general formulas Nd(La)Co_{1 + x} O_{3 + 1.5x} , or Nd_{1/(1 + x)}(La)_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)}, has been measured between 300 and 1050 K. The effective magnetic moments of paramagnetic ions have been determined in the temperature ranges of CurieWeiss behavior and have been used to evaluate the fractions of low-, intermediate-, and high-spin Co³⁺ ions. Raising the temperature from 320 to 660 K (non-Curie—Weiss behavior) increases the fraction of high-spin Co³⁺ ions in LaCo_{1 + x} O_{3 + 1.5x} (La_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)} from 27–43 to 56–61%. Moreover, in this temperature range the conductivity of the lanthanum cobaltites rises most steeply. In the range 660–950 K, no spin transition occurs in LaCo_{1 + x} O_{3 + 1.5x} , the slope of the conductivity versus temperature curves gradually decreases, and the conductivity gradually saturates. The conductivity of NdCo_{1 + x} O_{3 + 1.5x} (Nd_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)}) varies considerably in the range 550–950 K, and the spin transition in these cobaltites takes place between 260 and 760 K. Above 760 K, the NdCo_{1 + x} O_{3 + 1.5x} cobaltites with x = 0.05 and 0.10 contain, respectively, 72 and 83% high-spin Co³⁺ ions and 28 and 17% high-spin Co⁴⁺ ions, whereas neodymium cobaltite with x = 0.15 contains 83% high-spin and 17% intermediate-spin Co³⁺ ions. Original Russian Text ? S.V. Shevchenko, L.A. Bashkirov, G.S. Petrov, S.S. Dorofeichik, N.N. Lubinskii, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 1, pp. 88–94.     

Growth and Raman spectra of doped ZnO single crystals

ZnO:M ⁿ⁺(M ⁿ⁺ = Cd²⁺, Co²⁺, Ni²⁺, Sc³⁺, In³⁺, Ga³⁺, Fe³⁺, Te⁴⁺, V⁵⁺) single crystals have been grown under hydrothermal conditions in ZnO-M _x O _y -KOH-LiOH-H₂O systems, and their Raman spectra have been measured under visible (514.5 nm) and near-IR (1064 nm) excitation. The anomalous band between 500 and 600 cm⁻¹ in the Raman spectra of ZnO:Mn²⁺ has A ₁ symmetry and is due to vibrations involving Mn²⁺.     

Structural and magnetic properties of Ba0.7Sr0.3Fe12 − 2x Co x Ti x O19 M-type hexaferrites

We have studied the effect of “double” substitution in Ba_0.7Sr_0.3Fe_{12 ? 2x} Co _x Ti _x O₁₉ on the structural and magnetic properties of M-type barium hexaferrite. The basic composition of Ba_{1 ? x} Sr _x Fe₁₂O₁₉ obtained by heat-treating carbonate-hydroxide precipitates has been optimized (x = 0.3). 2Fe³⁺ → Co²⁺ + Ti⁴⁺ substitutions considerably reduce the coercive force (H _c) and increase the magnetization (M _s) relative to Ba_0.7Sr_0.3Fe₁₂ O₁₉.     

Peculiarities in the electrical and magnetic properties of cobalt perovskites Ln1−xMxCoO3 (Ln3+: La3+, M2+: Ca2+, Sr2+, Ba2+; Ln3+: Nd3+, M2+: Sr2+)

We refer here to the electrical and magnetic properties of the Ln_1−xM_xCoO₃ systems (Ln³⁺: La³⁺, M²⁺: Ca²⁺, Sr²⁺, Ba²⁺; Ln³⁺: Nd³⁺, M²⁺: Sr²⁺), paying special attention to those ferromagnetic compounds that display M–I transitions as temperature rises: La_1−xM_xCoO₃ (M²⁺: Ca²⁺, Sr²⁺, Ba²⁺) in the compositional interval x=0.2–0.3, and Nd_1−xSr_xCoO₃, with x=0.40. The magneto-transport properties of such materials are peculiar and interesting: they show diodic behavior and large relaxation effects — these latter being specially important in the Nd compound — they display magnetoresistive effects specially at the M–I transition temperatures, and they age with time. All these results are discussed on the basis of the inhomogeneous electronic structure of these doped cobalt perovskites and taking into account the influence of the lanthanide ion on their magnetic and electrical properties.     

Influence of Ag-doping in La0.5Sr0.5CoO3 on Its Structural and Magnetic Properties

The structural and magnetic properties of the mixed valent cobaltites La_0.5Sr_0.5?x Ag _x CoO₃ (0≤x≤0.15) with perovskite structure have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement shows that all our samples crystallize in the orthorhombic structure with $R\overline{3}c$ space group. Although the unit cell volume remains almost constant, the Co–O bond length and the Co–O–Co bond angle are sensitive to the Ag addition. All our studied samples undergo a paramagnetic-ferromagnetic transition with decreasing temperature. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT of La_0.5Sr_0.5CoO₃ (x=0) sample exhibits thermomagnetic irreversibility indicating frustration and competition of both antiferromagnetic and ferromagnetic interactions. It is suggested that Co³⁺ ions are in the intermediate spin state but Co⁴⁺ ions stay in a mixture of intermediate and high spin states. Ag addition leads to dramatic changes in magnetic properties. An interesting result has been obtained for La_0.5Sr_0.4Ag_0.1CoO₃, where the ZFC and FC curves coincide. For La_0.5Sr_0.35Ag_0.15CoO₃ (x=0.15) sample, the observed thermomagnetic irreversibility is much higher than that observed in x=0 sample. Hysteresis loops were recorded for x=0, 0.05, 0.1, and 0.15. The coercitive field is found to increase with Ag content reaching 0.26 T for x=0.15 whereas the remanent magnetization decreases.     

Electronic conduction in La-based perovskite-type oxides

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo_0.5Ni_0.5O_3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo_0.5Ni_0.5O_3±δ exhibits a high conductivity of 1.9 × 10³ S cm⁻¹ at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 10²² cm⁻³ and a small effective mass m∗ of 0.10 m_e. Notably, LaCo_0.5Ni_0.5O_3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo_0.5Ni_0.5O_3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La_1−xSr_xCoO_3±δ and La_1−xSr_xMnO_3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 10³ S cm⁻¹ for La_0.5Sr_0.5CoO_3±δ and 1.5 × 10³ S cm⁻¹ for La_0.6Sr_0.4MnO_3±δ because oxygen release occurs in La_1−xSr_xCoO_3±δ as elevating temperature and the electrical conductivity of La_0.6Sr_0.4MnO_3±δ slightly decreases at temperatures above 400 K.     

Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3

Abstract

The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr_1.261CoO₃ has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr_1.261CoO₃ is a composite crystal that consists of the [CoO₃] and [2Sr] subsystems. The [CoO₃] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO₆ polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO₃] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co–O bonds than the Oh sites: d_av. =2.039(4) Å (TP) and 1.895(3) Å (Oh). The averaged Co bond valences are Co^3.56(3)+ in the Oh sites and Co^2.45(3)+ in the TP sites, suggesting that a considerable amount of Co³⁺ ions are mixed with Co⁴⁺ions in the Oh sites and with Co²⁺ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S=0 low-spin state for Co³⁺(dε⁶), S=1/2 low-spin state for Co⁴⁺(dε⁵) and S=3/2 high-spin state for Co²⁺(dε⁵dγ²). The Weiss temperature, approximately 0.8 K, implies that Sr_1.261CoO₃ naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co³⁺ ions. These results suggest that the nonmagnetic Co³⁺ ions play an essential role in the magnetism of Sr_2γCoO₃ systems.     

The magnetic properties of Bi0.9Ba0.1Fe0.81M0.09Ti0.1O3 solid solutions (M = Co, Mn, Sc, Al)

Solid solutions with general formula Bi_0.9Ba_0.1Fe_0.81M_0.09Ti_0.1O₃ (M = Co, Mn, Sc, Al) together with parental Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ were prepared by the traditional solid state reaction method. Their structural, room temperature magnetic, and dielectric properties were investigated. X-ray diffraction analysis indicated that all samples maintained original R3c space group. M–H hysteresis loop of Co³⁺ doped sample saturated at an applied field of 1 T with spontaneous magnetization of 1.735 emu/g, while Mn⁴⁺ substitution enhanced the magnetization of Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ less strongly; addition of Sc³⁺ helped decrease magnetic coercive field while Al³⁺ modified sample exhibited paramagnetic M–H hysteresis loop. Differential scanning calorimetry was applied to determine the Neel temperature (T_N) and the T_N for undoped, Co³⁺, Mn⁴⁺, Sc³⁺, Al³⁺ doped solid solutions were 318.1, 324.3, 335.7, 293.9 and 295.8 respectively. Sc³⁺ substitution had little influence on the dielectric properties of Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ while Al³⁺ doping improved its dielectric constant. In contrast, Co³⁺, Mn⁴⁺ doped samples showed decreased permittivity but inhibited tan δ at frequencies larger than 30 kHz.     

Luminescence characterization of (Ca1−xSrx)(S1−ySey):Eu,M (M = Sc and Y) for high color rendering white LED

The highly efficient red phosphors (Ca_1−xSr_x)(S_1−ySe_y):Eu²⁺,M³⁺ (M = Sc and Y) were prepared, starting from CaCO₃, SrCO₃, Eu₂O₃, Sc₂O₃, Y₂O₃, S, and SeO₂ with a flux, by a conventional solid-state reaction. The optimized red phosphors converted 11.8% (Sc³⁺) and 11.7% (Y³⁺) of the absorbed blue light into luminescence. These quantum values are much higher than Q = 3.0% of CaS:Eu²⁺. For the fabrication of light-emitting diodes (LEDs), the prepared phosphors were coated with MgO from non-aqueous solution to overcome their weakness against moisture. White LEDs were fabricated by pasting the prepared red phosphors and the yellow YAG:Ce³⁺ phosphor on an InGaN blue chip (λ_ems = 446.5 nm). The incorporation of the red phosphor to the YAG:Ce³⁺ phosphor resulted in an improved color rendering index (Ra) from 70 to 80.     

Dielectric properties of (1−x)(Mg0.95Co0.05)TiO3-xCaTiO3 ceramic system at microwave frequency

The microwave dielectric properties and the microstructures of the (1−x)MgTiO₃-xCaTiO₃ ceramic system were investigated. With partial replacement of Mg by Co, dielectric properties of the (1−x)(Mg_0.95Co_0.05)TiO₃-xCaTiO₃ ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature. At 1275°C, the 0.95(Mg_0.95Co_0.05)TiO₃-0.05CaTiO₃ ceramics possesses excellent microwave dielectric properties: a dielectric constant ε_r of 20.3, a Q×f value of 107 000 ( at 7 GHz) and a τ_f value of −22.8 ppm/°C. By appropriately adjusting the x value in the (1−x)(Mg_0.95Co_0.05)TiO₃-xCaTiO₃ ceramic system, zero τ_f value can be achieved. With x=0.07, a dielectric constant ε_γ of 21.6, a Q×f value of 92 000 (at 7 GHz) and a τ_f value of −1.8 ppm/°C was obtained for 0.93(Mg_0.95Co_0.05)TiO₃-0.07CaTiO₃ ceramics sintered at 1275°C for 4 h.     

Studying trivalent/bivalent metal ion doped TiO2 as p-TiO2 in bipolar heterojunction devices

Trivalent/bivalent metal ions doped TiO₂ thin films (M_xTi_1−xO₂, M = Cr³⁺, Fe³⁺, Ni²⁺, Co²⁺, Mn²⁺ and x = 0.01, 0.05, 0.1, 0.15, 0.2) were deposited on Indium–tin oxide (ITO) coated glass substrates by spin coating technique. X-ray photoelectron spectroscopy (XPS) showed Ti⁴⁺ oxidation state of the Ti2p band in the doped p-TiO₂. The homogenous M_xTi_1−xO₂ was used to support n-ZnO thin films with thickness ∼40–80 nm and vertically aligned n-ZnO nanorods (NR) with length ∼300 nm and 1.5 μm. Current (I)–voltage (V) characteristics for the Ag/n-ZnO/M_xTi_1−xO₂/ITO/glass assembly showed rectifying behavior with small turn-on voltages (V₀) < 1 V. The ideality factor (η) and the resistances in both forward and reverse bias were calculated. The temperature dependence performance of these bipolar devices was performed and variation of the parameters with temperature was studied.     

Shaped single crystal growth and scintillating application of Yb:(Gd,Lu)3(Ga,Al)5O12 solid solutions

Shaped single crystals of (Yb_0.05Lu_xGd_0.95−x)Ga₅O₁₂ (0.0x0.9) and Yb_0.15Gd_0.15Lu_2.7(Al_xGa_1−x)O₁₂ (0.0x1.0) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)₃(Ga,Al)₅O₁₂ are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd³⁺ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd³⁺ or Yb³⁺ cations below 240 nm. A complete absence of Yb³⁺ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb³⁺ by that of Gd³⁺ ions. For specific composition of Lu_1.5Gd_1.5Ga₅O₁₂ an intense defect––host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi₄Ge₃O₁₂, was found.     

Studies on LiNi0.7Al0.3−xCoxO2 solid solutions as alternative cathode materials for lithium batteries

A series of phase-pure Co- and Al-substituted lithium nickel oxide solid solutions of the composition LiNi_0.7Al_0.3−xCo_xO₂ with x=0.0, 0.1, 0.15, 0.2, and 0.3, has been synthesized by adopting urea-assisted combustion (UAC) route. The structure and the physico-electrochemical features of the doped materials have been evaluated through PXRD, FTIR, SEM, CV, and charge/discharge studies. The stabilization of Ni in the +3 state and the existence of enhanced 2D-layered structure without any cation mixing have been substantiated from XRD. The results of the XRD and FTIR studies have established the complete mixing of Al and Co with Ni, especially at the various levels and the combinations of the dopants attempted in the present study. The enhanced electrochemical performance of LiNi_0.7Al_0.3−xCo_xO₂ may be attributed to the “synergetic effect” resulting from the presence of both Al³⁺ and Co³⁺ dopants in the LiNiO₂ matrix. From CV studies, it was understood that the addition of 10% Co is effective in suppressing the phase transformation during Li⁺ intercalation process that leads to better electrochemical properties. The effect and the extent of substitution of Ni with Al and Co on the structural and electrochemical performance of LiNi_0.7Al_0.3−xCo_xO₂ are discussed elaborately in this communication.     

Controlled processing of (Gd,Ln)2O3:Eu (Ln = Y,Lu) red phosphor particles and compositional effects on photoluminescence

Synthesis of (Gd_0.95−xLn_xEu_0.05)₂O₃ (Ln = Y and Lu, x = 0–0.95) powders via ammonium hydrogen carbonate (AHC) precipitation has been systematically studied. The best synthesis parameters are found to be an AHC/total cation molar ratio of 4.5 and an ageing time of 3 h. The effects of Y³⁺ and Lu³⁺ substitution for Gd³⁺, on the nucleation kinetics of the precursors and structural features and optical properties of the oxides, have been investigated. The results show that (i) different nucleation kinetics exist in the Gd–Y–Eu and Gd–Lu–Eu ternary systems, which lead to various morphologies and particle sizes of the precipitated precursors. The (Gd,Y)₂O₃:Eu precursors display spherical particle morphologies and the particle sizes increase along with more Y³⁺ addition. The (Gd,Lu)₂O₃:Eu precursors, on the other hand, are hollow spheres and the particle sizes increase with increasing Lu³⁺ incorporation, (ii) the resultant oxide powders are ultrafine, narrow in size distribution, well dispersed and rounded in particle shape, (iii) lattice parameters of the two kinds of oxide solid solutions linearly decrease at a higher Y³⁺ or Lu³⁺ content. Their theoretical densities linearly decrease with increasing Y³⁺ incorporation, but increase along with more Lu³⁺ addition and (iv) the two kinds of phosphors exhibit typical red emissions at ∼613 nm and their charge-transfer bands blue shift at a higher Y³⁺ or Lu³⁺ content. Photoluminescence/photoluminescence excitation intensities and external quantum efficiency are found to decrease with increasing value of x, and the fluorescence lifetime mainly depends on the specific surface areas of the powders.     

Synthesis of an oxygen nonstoichiometric Sr6Co5O15 phase

Sr₆Co₅O₁₅, a member of the (A₃Co₂O₆)_m(A₃Co₃O₉)_n [A = Ca, Sr, Ba] series, showed oxygen nonstoichiometry. Sr₆Co₅O_15.12, Sr₆Co₅O_14.98, Sr₆Co₅O_14.45 and Sr₆Co₅O_14.26 were prepared by a solid state reaction in air. The Sr₆Co₅O₁₅ phase is stable in the temperature range of 873–973 K in air, there are structure transitions at 773 K and above 1023 K. With the loss of oxygen, the a-axis parameter of the Sr₆Co₅O₁₅ phase decreased from 9.4988(3) Å (Sr₆Co₅O_15.12) to 9.4390(4) Å (Sr₆Co₅O_14.26) and the c-axis parameter increased from 12.3772(3) Å (Sr₆Co₅O_15.12) to 12.5066(4) Å (Sr₆Co₅O_14.26) with decreasing oxygen content. The Rietveld analysis of the powder X-ray diffraction data suggested that the increase in the c-axis was mainly due to the increase in the CoCo distance between the CoO₆ trigonal prism and CoO₆ octahedron.     

Synthesis of cobalt-aluminum spinels via EDTA chelating precursors

In this work, synthesis of nanocrystalline Co^||Co^||| _x Al_2–x O₄ (where x = 0, 0.5, 0.8, 1, 1.18 and 2) spinels by the thermal decomposition of complex precursors derived from metal nitrate salts and ethylenediaminetetraacetic acid (EDTA) has been systematically studied. Based on XRD, FTIR, DTA, TGA, SEM and TEM analyses, it has been found that the as-prepared metal organic precursors with different Co and Al contents display different thermal behavior and crystal development and particle morphology. Increment of Co content in precursors improves the degree of crystallinity of the powder. Treated at 400°C, in contrast to the well formed Co₃O₄ or Co₃O₄-like spinel structure for the powder precursors containing higher Co content, most of the powders from precursors containing lower Co content are still amorphous. Higher Co content in the precursors slightly decreases the unit cell parameters of the resulting Co^||Co^||| _x Al_2–x O₄ spinels. Prepared at 900°C, the unit cell parameters of Co^||Al₂O₄, Co^||Co^||| _0.5Al_1.5O₄, Co^||Co^|||AlO₄, Co^||Co^||| ₂O₄ are 8.1038, 8.1007, 8.0867, and 8.0834 Å, respectively. Based on this work, preparation of a series of the Co^||Co^||| _x Al_2–x O₄ spinels including black or bright blue Co^||Al₂O₄, Co^||Co^||| _0.5Al_1.5O₄, Co^||Co^|||AlO₄, Co^||Co^||| ₂O₄ from EDTA-Co(Al) complexing precursor has been established.     

Magnetic properties of LaInO<Subscript>3</Subscript>-based perovskite-structure photoluminescent materials doped with Nd<Superscript>3+</Superscript>, Cr<Superscript>3+</Superscript>, and Mn<Superscript>3+</Superscript> ions

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.