Atom states and interatomic interactions in perovskite-like oxides: XXXV. Magnetic properties of solid solutions of lanthanum manganites doped with ytterbium and calcium in LaAlO<Subscript>3</Subscript>

The solid solutions La_1–YYb_yAlO₃ (y = 0.01–0.20) and La_1–0.397xYb_0.067xCa_0.33xMn_xAl_1–xO₃ (x = 0.01–0.10) were studied by magnetic dilution method. The state of paramagnetic elements and the character of exchange interactions between them were determined on the basis of examination of magnetic properties. Clustering of manganese atoms in the La_1–0.397xYb_0.067xCa_0.33xMn_xAl_1–xO₃ solid solution, as distinct from the La_1–0.67xCa_0.33xMn_xAl_1–xO₃ solid solutions studied before, is determined by the presence of ytterbium atoms in the perovskite structure of the complex oxides under study.     

Synthesis and properties of fuel cell anodes based on (La0.5 + x Sr0.5 − x )1 − y Mn0.5Ti0.5O3 − δ (x = 0–0.25, y = 0–0.03)

Results are presented of studying electrochemical properties of perovskite-like solid solutions (La_{0.5 + x} Sr_{0.5 ? x} )_{1 ? y} Mn_0.5Ti_0.5O_{3 ? δ} (x = 0–0.25, y = 0–0.03) synthesized using the citrate technique and studied as oxide anodic materials for solid oxide fuel cells (SOFC). X-ray diffraction (XRD) analysis is used to establish that the materials are stable in a wide range of oxygen chemical potential, stable in the presence of 5 ppm H₂S in the range of intermediate temperatures, and also chemically compatible with the solid electrolyte of La_0.8Sr_0.2Ga_0.8Mg_0.15Co_0.05O_{3 ? δ} (LSGMC). It is shown that transition to a reducing atmosphere results in a decrease in electron conductivity that produced a significant effect on the electrochemical activity of porous electrodes. Model cells of planar SOFC on a supporting solid-electrolyte membrane (LSGMC) with anodes based on (La_0.6Sr_0.4)_0.97Mn_0.5Ti_0.5O_{3 ? δ} and (La_0.75Sr_0.25)_0.97Mn_0.5Ti_0.5O_{3 ? δ} and a cathode of Sm_0.5Sr_0.5CoO_{3 ? δ} are manufactured and tested using the voltammetry technique.     

Phase equilibria in the system LaMnO<Subscript>3</Subscript>-SrMnO<Subscript>3</Subscript>-SrCrO<Subscript>4</Subscript>-LaCrO<Subscript>3</Subscript>

A continuous solid solution LaMn_1?y Cr _y O₃ with an orthorhombic structure is found to exist in the range of 0.0 ≤ y ≤ 1.0. An orthorhombic solid solution La_1?x Sr _x CrO₃ exists in the range of 0.0 ≤ x ≤ 0.1. The stability boundaries are determined for the perovskite phase La_1?x Sr _x Mn_1?y Cr _y O₃. An isobaric-isothermal section LaMnO₃-SrMnO₃-SrCrO₄-LaCrO₃ of the system La₂O₃-SrO-Mn₃O₄-Cr₂O₃ in air at 1100°C is designed.     

Regions of stability of variable-composition perovskite phases La1?xSrxMn1?yMyO3 (M = Ti, Ni)

The formation of the orthorhombic solid solution series LaMn_1−y Ti _y O₃ with 0.0 ≤ y ≤ 0.15 and LaMn_1−y Ni _y O₃ with 0.0 ≤ y ≤ 0.4 was observed. The stability boundaries of the La_1−x Sr _x Mn_1−y M _y O₃ (M = Ti, Ni) perovskite phases were determined. Fragments of isobaric-isothermal sections of the phase diagrams of the La₂O₃-SrO-Mn₃O₄-TiO₂ and La₂O₃-SrO-Mn₃O₄-NiO systems in air at 1100°C were suggested. Original Russian Text ? E.A. Filonova, A.N. Demina, A.N. Petrov, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 10, pp. 1787–1790.     

Crystal Structure and Property of Perovskite-Type Oxides Containing Ion Vacancy

Studies on the role of oxygen vacancy in structural change of nonstoichiometric perovskites and a property of oxygen-deficient perovskite-related K₂NiF₄ compounds are reviewed.The structural changes on which the authors focused are cation ordering and lattice distortion. The relationship between the distortion and oxygen vacancy was investigated by comparing the structures of Sr₂(Sr_1-xM_x)TaO_6-d (M = Ca²⁺ and Nd³⁺) solid solutions. It was found that distortion of a perovskite-type lattice decreased with an increasing amount of oxygen vacancies. In order to investigate the relationship between the cation ordering on octahedral sites and oxygen vacancy, structures of stoichiometric Sr_2-xLa_xCo_1-yTa_1+yO₆ and oxygen-deficient Sr_2-xLa_xMg_1-yTa_1+yO_6-d solid solutions were compared. The authors' work reveals that the cation ordering affects the amount of oxygen vacancies in addition to cation charge and size.     

Phase Equilibria and Crystal Structure of Complex Oxides in the La–Sr–Co–Ni– System

Phase equilibria in the La–Sr–Co–Ni–O system were studied in air at 1100°. The samples for the study were synthesized by the standard ceramic and citrate processes. The limiting solubility and structure of La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were determined by Xray powder diffraction analysis. La_1-xSr_xCo_1-yNi_yO₃- solid solutions with 0 x 0.5 have a distorted rhombohedral perovskitelike structure (R c space group). An increase in the strontium concentration reduces the rhombohedral distortions, and the compounds with x < 0.5 have an ideal cubic structure (Pm3m space group). (La_1-xSr_x)₂Co_1-yNi_yO₄ crystals have a tetragonal K₂NiF₄ type unit cell (I4/mmm space group). The relationships between unit cell parameters and compositions were obtained for singlephase La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ samples. The existence regions of La_1-xSr_xCo_1-yNi_yO₃- and La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were distinguished on P–T phase diagrams.     

Cation distribution and interatomic interactions in oxides with heterovalent isomorphism: XII. Gd2Sr1? x Ca x Al2O7 solid solutions

The area of existence of Gd₂Sr_1−x Ca _x Al₂O₇ solid solutions at x ≤ 0.5 was determined by the X-ray phase analysis. It was found by full-profile X-ray structural analysis that, in contrast to La₂Sr_1−x Ca _x Al₂O₇ solid solutions, the Ca²⁺ cations occupy not only AO₉ nine-vertex fragments, but also AO₁₂ oxygen cubooctahedra. Full ordering of Sr²⁺ cations in the perovskite layer is observed at the calcium content x 0.5. Original Russian Text ? I.A. Zvereva, A.G. Cherepova, Yu.E. Smirnov, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 4, pp. 557–563. For communication XI, see [1].     

Neutron powder diffraction investigations of hydrogenated Pd3P0.80 and Pd6P

The solid solutions Sr_3?xLa_xMn₂O₇ (0 ≤ x ≤ 1.50) and Sr_3?xLn_xMn₂O₇ (Ln = Nd, Sm, Gd; 0 ≤ x ≤ 1.40) with Sr₃Ti₂O₇-type structure have been prepared. Their cell parameters and $\text{c}\text{a}$ ratios are related to the size of the rare earths and to the Mn³⁺ ion concentration.     

Phase equilibria in the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system and interactions of phases with H2SO4 and NaOH solutions

Phase composition of the V₂O₅-NaVO₃-Ca(VO₃)₂-Mn₂V₂O₇ system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca_1–x Mn _x (VO₃)₂ solid solution is in equilibrium with all compounds of the system (V₂O₅, NaVO₃, Ca(VO₃)₂), vanadium β-bronzes Na _x V₂O₅ (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn₂V₂O₇, and Na₂Mn₃(V₂O₇)₂ and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na₂Ca(VO₃)₄ is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO₃)₂ increases α in aqueous NaOH to 20%. For Na₂Mn₃(V₂O₇)₂, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%.     

Synthesis and properties of colored copper-containing alkaline-earth phosphates with an apatite structure

Colored compounds A₅(PO₄)₃Cu_0.1OH _z , where A = Ba_1-x Sr _x (x=0,0.5,0.8), Sr_1-y Ca _y (y=0,0.2, 0.5, 1), and Ba_1/3Sr_1/3Ca_1/3 with an apatite structure containing copper ions in the hexagonal channels have been synthesized by the thermal treatment of the corresponding carbonates, oxides, and ammonium hydrophosphate at 1150°C. The use of the composition with A = Ba_0.5Ca_0.5 gives a multiphase product containing apatite (Ba_1-x Ca _x )₅(PO₄)₃Cu _y OH _z with x ∼ 0.2 as the major phase. The hexagonal lattice parameters of apatite depend linearly on the content of solid solution in the alkaline-earth metals. In the series of A = Ba, Ba-Sr, Sr, Sr-Ca, and Ca, the color of the samples changes smoothly from blue through violet to pink, whereas the samples with A = Ba_0.5Ca_0.5 and Ba_1-3Sr_1-3Ca_1-3 are light gray. The diffuse reflectance electronic spectra exhibit two absorption bands characteristic of the copper ions in the hexagonal channels. Their positions depend on the alkaline-earth metal content of the compound. The third characteristic band appears in the spectrum of calcium apatite. Its relative intensity increases when calcium is gradually replaced by strontium and especially by barium, which results in worsening and even loss of the sample color. These spectral changes are presumably due to the transition of some copper ions from the hexagonal channels to other positions of the crystal lattice.     

Cation Distribution and Interatomic Interactions in Oxides with Heterovalent Isomorphism: VI. Solid Solutions Nd2Sr1 - xCaxAl2O7

The range of existence of Nd₂Sr_{1 - x} Ca _x Al₂O₇ solid solutions (x 0.5) was established. The distribution of neodymium, strontium, and calcium cations over two structural sites was studied by full-profile X-ray analysis. Unlike La₂Sr_{1 - x} Ca _x Al₂O₇ solid solutions, Ca^{2 +} cations fill not only nine-vertex AO₉ polyhedra, but also oxygen cubic octahedra AO_{1 2}. Introduction of calcium results in disordered distribution of Nd^{3 +} cations, destabilization of the layered structure, and decomposition of the solid solutions.     

Thermochemistry of La0.7Sr0.3Mn1−xFexO3 solid solutions (0<x<1)

The structure, the energetics and the internal redox reactions of La_0.7Sr_0.3Fe_xMn_1−xO₃ have been studied in the complete solid solution range 0.0<x<1.0. High temperature oxide melt drop solution calorimetry was performed to determine the enthalpies of formation from binary oxides and the enthalpy of mixing. There is a noticeable change in the energetics of the solid solution near x=0.7, which is due to the growing concentration of Fe⁴⁺ at higher Fe/(Fe+Mn) ratio. The balance between different valences of the transition metals, Mn and Fe, is the main factor in determining the energetics of the La_0.70Sr_0.30Fe_xMn_1−xO₃ solid solution.     

Control of Oxidation States of Transition Elements (Cr,Mn) in Nitridometalates and the Solid Solution Series Li6(Ca1‐xSrx)2[Mn2N6]

The formation of ternary nitridometalates from the elements in the case of the systems Li—Cr, V, Mn—N leads to compounds which contain the transition metals in the highest (V^V, Cr^VI) or a comparably high (Mn^V) oxidation state. In the corresponding calcium and strontium systems, the transition metals show a lower oxidation state (V^III, Cr^III, Mn^III). Transition metals with intermediate oxidation states (Cr^V, Mn^IV) are present in the quaternary (mixed cation) compounds Li₄Sr₂[CrN₆], Li₆Ca₂[MnN₆], and Li₆Sr₂[MnN₆] (R3¯(#148), a = 585.9(3) pm, c = 1908.6(4) pm, Z = 3), as well as in the solid solution series Li₆(Ca_1—xSr_x)₂[MnN₆].     

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of Ln1 ? xSrxGa0.5 ? y/2Al0.5 ? y/2MgyO3 ? δ (Ln = La, Pr, Nd; x, y = 0.10, 0.15)

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of samples of Ln_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} (Ln = La, Pr, Nd; x, y = 0.10, 0.15) synthesized by a ceramic methods are studied. Methods of x-ray diffraction analysis and scanning electron microscopy reveal the La-containing samples to be homogeneous and have a perovskite structure. Magnesium does not dissolve in Pr-and Nd-containing systems but forms an individual phase based on magnesium oxide. Apart from magnesium oxide, in these systems there form extrinsic phases, specifically, LnSrGa₃O₇ and an unknown phase. The electroconductivity of La_{1 − x} Sr_xGa_{1 − y} Mg_yO_{3 − δ} decreases after substituting Al for Ga. Ceramic La_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_3−δ is a purely ionic conductor in the temperature interval 500 to 1000°C; Nd_xSr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} has predominantly ionic conduction; and the predominant type of conduction in Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} is electronic below 700–800°C, with the contribution of ionic conduction increasing at higher temperatures. Substituting Al for Ga raises the hardness of ceramics under study. Among the compositions studied, La_0.85Sr_0.15Ga_0.45Al_0.45Mg_0.10O_{3 − δ} and La_0.85Sr_0.15Ga_0.425Al_0.425Mg_0.15O_{3 − δ} exhibit a combination of electroconductivity and hardness that is optimal for application as electrolyte at reduced temperatures (600–800°C). The Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} system possesses mixed ionic-electronic conduction and high hardness, which makes it appealing for application as oxygen-penetrable membranes. Original Russian Text ? Yu.V. Danilov, A.D. Neuimin, L.A. Dunyushkina, L.A. Kuz’mina, N.S. Zybko, Z.S. Martem’yanova, A.A. Pankratov, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 1, pp. 57–65.     

Synthesis and structural characterization of LaxSr1−xMnO2.6+δ (0.1<x<0.4) compounds displaying compressed octahedral coordination of Mn

La_xSr_1−xMnO_2.6+δ (x=0.1-0.4) compounds have been obtained by low-temperature annealing of stoichiometric materials in hydrogen. La_0.1Sr_0.9MnO_2.6+δ (δ=0.15) and La_0.3Sr_0.7MnO_2.6, tetragonal (P4/m), and La_0.2Sr_0.8MnO_2.6, pseudo-tetragonal monoclinic (P2/m), structures are isostructural with oxygen-vacancy-ordered Sr₅Mn₅O₁₃ (, c≈a_P). La_0.4Sr_0.6MnO_2.6 shows cubic perovskite structure with disordered oxygen vacancies. In the vacancy-ordered (La_xSr_1−x)₅Mn₅O₁₃ phases four out of five Mn cations are Mn³⁺ and show a typical Jahn-Teller elongated pyramidal coordination while the fifth one Mn^(4−5x)+, in octahedral environment, shows decreasing formal charge from Mn⁴⁺ (x=0) to Mn^2.5+x=0.3. This unusual selective doping of the octahedral site produces structural strain due to increasing size of the Mn^(4−5x)+ and, in the case of (La_0.2Sr_0.8)₅Mn₅O₁₃, the unusual compressed octahedral arrangement of oxygen atoms around it. The coordination geometry implies that either the d_x²-y² orbital is occupied, which would be a rare example of inverted occupancy of e_g orbitals in manganites, or that disordered Mn³⁺ apically elongated MnO₆ octahedra are present with normal electronic configuration , and the observed bond distances are the average of the long and intermediate in-plane Mn-O bonds. Several structural features favor the second case.     

Crystal structure and electrical conductivity of lanthanum-calcium chromites-titanates La1−xCaxCr1−yTiyO3−δ (x=0-1, y=0-1)

Five series of perovskite-type compounds in the system La_1−xCa_xCr_1−yTi_yO₃ with the nominal compositions y=0, x=0-0.5; y=0.2, x=0.2-0.8; y=0.5, x=0.5-1.0; y=0.8, x=0.6-1.0 and y=1, x=0.8-1 were synthesized by a ceramic technique in air (final heating 1350 °C). On the basis of the X-ray analysis of the samples with (Ca/Ti)?1, the phase diagram of the CaTiO₃-LaCr^IIIO₃-CaCr^IVO₃ quasi-ternary system was constructed. Extended solid solution with a wide homogeneity range is formed in the quasi-ternary system CaCr^IVO₃-CaTiO₃-LaCr^IIIO₃. The solid solution La_{(1−x′−y)}Ca_(x′+y)Cr^IV_x′Cr^III_{(1−x′−y)}Ti_yO₃ exists by up to 0.6-0.7 mol fractions of CaCr^IVO₃ (x^′<0.6-0.7) at the experimental conditions. The crystal structure of the compounds is orthorhombic in the space group Pbnm at room temperature. The lattice parameters and the average interatomic distances of the samples within the solid solution ranges decrease uniformly with increasing Ca content. Outside the quasi-ternary system, the nominal compositions La_0.1Ca_0.9TiO₃, La_0.2Ca_0.8TiO₃, La_0.4Ca_0.6Cr_0.2Ti_0.8O₃ and La_0.3Ca_0.7Cr_0.2Ti_0.8O₃ in the system La_1−xCa_xCr_1−yTi_yO₃ were found as single phases with an orthorhombic structure. In the temperature range between 850 and 1000 °C, the synthesized single-phase compositions are stable at pO₂=6×10⁻¹⁶-0.21×10⁵ Pa. Oxygen stoichiometry and electrical conductivity of the separate compounds were investigated as functions of temperature and oxygen partial pressure. The chemical stability of these oxides with respect to oxygen release during thermal dissociation decreases with increasing Ca-content. At 900 °C and oxygen partial pressure 1×10⁻¹⁵-0.21×10⁵ Pa, the compounds with x>y (acceptor doped) are p-type semiconductors and those with x<y (donor doped) and x=y are n-type semiconductors. The type and level of electrical conductivity are functions of the concentration ratios of cations occupying the B-sites of the perovskite structures: [Cr³⁺]/[Cr⁴⁺] and [Ti⁴⁺]/[Ti³⁺]. The maximum electrical conductivity at 900 °C and pO₂=10⁻¹⁵ Pa was found for the composition La_0.1Ca_0.9TiO₃ (near 50 S/cm) and in air at 900 °C for La_0.5Ca_0.5CrO₃ (close to 100 S/cm).     

Reactions between YBa2Cu3O7−δ and La2O3 and SrCO3

Solid state reactions at 925°C between the high-T _c ceramic superconductor YBa₂Cu₃O_7?δ and La₂O₃ and SrCO₃, respectively, mixed in various molar ratiosr=MeO_n/YBa₂Cu₃O_7?δ, were studied using X-ray powder diffraction and scanning electron microscopy. The reaction between YBa₂Cu₃O_7?δ and La₂O₃ yielded (La_1?xBa_x)₂CuO_4?δ, withx≈0.075?0.10. La_2?xBa_1+xCu₂O_6?δ, withx≈0.2?0.25 and La-doped (Y_1?xLa_x)₂BaCuO₅, withx≈0.10?0.15. Forr=3.0, Y-doped La₂BaCuO₅ resulted also. The reaction between YBa₂Cu₃O_7?δ and SrCO₃ yielded (Sr_1?zBa_z)₂CuO₃, withz≈0.1, Y₂(Ba_1?zSr_z)CuO₅, withz=0.1?0.15, and a nonsuperconducting compound with an approximate composition of Y(Ba_0.5Sr_0.5)₅Cu_3.5O_10±δ. At values ofr≤2.0, unsubstituted YBa₂Cu₃O_7?delta was found in the reaction products.     

State of atoms and interatomic interactions in complex perovskite-like oxides: XXX. Influence of the nature of diamagnetic substituents on the dynamics of clustering in lanthanum gallate doped with strontium,chromium, and magnesium

The fractions of clusters and single chromium atoms were calculated by the diluted solution and Heisenberg-Dirac-van-Vleck models for a series of solid solutions containing chromium, strontium, and magnesium in the ratio 5:1:1, respectively. A principal genetic relationship was revealed between La_1−0.2x Sr_0.2x ·Cr _x Ga_1−x O_3−δ, La_1−0.5x Sr_0.5x Cr _x Ga_1−x O_3−δ, and La_1−0.2x Sr_0.2x Cr _x Ga_1−1.2x Mg_0.2x O_3−δ systems. Deviations from Curie-Weiss law are observed for the systems with the ratio [Cr]:[Sr]:[Mg]=5:1:1, which point to a noncompensated magnetic moment.     

Oxygen nonstoichiometry and defect structure analysis of B-site mixed perovskite-type oxide (La, Sr)(Cr, M)O3−δ (M=Ti, Mn and Fe)

The defect chemical relationships in various B-site mixed LaCrO₃-based ceramics were investigated by means of high-temperature gravimetry. The nonstoichiometric deviation, δ, in (La_0.7Sr_0.3)(Cr_1−yTi_y)O_3−δ (y=0.1, 0.2 and 0.3) (LSCT)_, (La_0.75Sr_0.25)(Cr_0.5Mn_0.5)O_3−δ (LSCM) and (La_0.75Sr_0.25)(Cr_0.5Fe_0.5)O_3−δ (LSCF) were measured as a function of oxygen partial pressure, P_O2, at temperatures between 973 and 1373 K.The effects of partial replacement of the donor on Cr-sites were examined in LSCT. In LSCM and LSCF, effects of the partial substitution of isovalent transition metals on Cr-sites are discussed. Oxygen nonstoichiometries of various B-site mixed LaCrO₃-based ceramics were compared with those of A-site substituted perovskite-type oxides, (La_1−xSr_x)MO_3−δ (where x=0-0.3, M=Cr, Mn and Fe). The partial substitution of the different elements on Cr-sites drastically changed the P_O2 and temperature dependence of oxygen vacancy formation in LaCrO₃-based ceramics. The defect equilibrium relationships of the localized electron well explained the oxygen vacancy formation in B-site mixed LaCrO₃-based ceramics. Oxygen vacancy formation in (La_0.7Sr_0.3)(Cr_1−yTi_y)O_3−δ (y=0.1 and 0.2) and (La_0.7Sr_0.3)(Cr_0.7Ti_0.3)O_3−δ was explained by redox reaction of Cr and Ti ions, respectively. The defect equilibrium relationships of LSCM and LSCF were interpreted by redox reaction of Mn ions and Fe ions, respectively. No significant change in valence state of Cr³⁺ ions in LSCM and LSCF was confirmed under the experimental conditions.     

Hexaferrites and phase relations in the iron-rich part of the system Sr-La-Co-Fe-O

The iron rich part of the system was examined in the temperature range of 1200-1380 °C in air, with focus on the solid solutions of M-type hexaferrites. Samples of suitable compositions were studied by electronprobe microanalysis (EPMA). Substituted Sr-hexaferrites in the system Sr-La-Co-Fe-O do not follow the 1:1 substitution mechanism of La/Co in M-type ferrites. Due to the presence and limited Co²⁺-incorporation Fe³⁺-ions are reduced to Fe²⁺ within the crystal lattice to obtain charge balance. In all examined M-type ferrites divalent iron is formed, even at 1200 °C. The substitution principle Sr²⁺+Fe³⁺↔La³⁺+(Fe²⁺, Co²⁺) yields to the general substitution formula for the M-type hexaferrite Sr²⁺_1-xLa³⁺_xFe²⁺_x-yCo²⁺_yFe³⁺_12-xO¹⁹ (0≤x≤1 and 0≤y≤x). In addition Sr/La-perovskite_SS (_SS=solid solution), Co/Fe-spinel_SS, hematite and magnetite are formed. Sr-hexaferrite exhibits at 1200 °C a limited solid solution with small amounts of Fe²⁺ (SrFe₁₂O₁₉↔Sr_0.3La_0.7Co_0.5Fe²⁺_0.2Fe_11.3O₁₉). At 1300 and 1380 °C a continuous solid solution series of the M-type hexaferrite is stable. SrFe₁₂O₁₉ and LaCo_0.4Fe²⁺_0.6Fe₁₁O₁₉ are the end members at 1300 °C. The maximum Fe²⁺O content is about 13 mol% in the M-type ferrite at 1380 °C (LaCo_0.1Fe²⁺_0.9Fe₁₁O₁₉).