A wide series of substitutions in a subsystem of small radii cations M = Al, Cr, Fe, Ga, Sc is possible in rare-earth borates ReM3(BO3)4 with the huntite structure. However, the existence of these compounds where M = Mn still raises doubts. The study presents a synthetic approach developed in the framework of the flux method allowing for the required conditions for introducing Mn into the huntite structure and growing single crystals from the GdFe3-& khcy;Mnx(BO3)4 solid solution. Special attention is paid to the choice of the solvent and elaboration of intermediate chemical bonds formed between the components of the solvent and crystal-forming part during synthesis. The explored flux composition based on Bi2O3-B2O3-Na2O (with the 1: 23.3: 2.66 molar ratio) allows obtaining isometric dark-brown crystals of GdFe3-& khcy;Mnx(BO3)4 slightly elongated along the c axis, with x = 0.27 and the size up to 5 & times; 4 & times; 4 mm3. The X-ray powder analysis confirms the structure to be identical to that of pure GdFe3(BO3)4. Notably, their lattice parameters change despite the equivalence of the ionic radii of Fe3+ and Mn3+ cations. The analysis of the thermal and field magnetization dependences of the synthesized GdFe3-& khcy;Mnx(BO3)4 reveals a series of low-temperature features in the form of a shift of the temperatures TN and TSR as compared to those characteristic for unsubstituted GdFe3(BO3)4 and a new feature is observed to appearat T1 = 16 K to a cascade of phase transitions due to the presence of manganese in the structure.

Targeted Ni 2+ doping shifts the Co 3− x Ni x B 2 O 6 –Co 3− x Ni x BO 5 phase boundary and enables reversible switching at Co 3 B 2 O 6 –Co 3− x Ni x BO 5 –Ni 3 B 2 O 6 triple point at x = 1. The precise synthesis control and redox management in cobalt materials are demonstrated.

Cobalt-containing borates are emerging as multifunctional materials for optical devices, Li-ion and Na-ion battery anodes, and rare-earth-free permanent magnets. In particular, the phases Co2B2O5, Co3B2O6 and Co3BO5 - which incorporate Co2+ and Co3+ centers - can all be crystallized from closely related Bi2O3-MoO3-Na2O-B2O3 fluxes with only minimum compositional adjustments. In this study, we elucidate (1) high-temperature crystallization pathways in these multicomponent flux systems and (2) factors that stabilize Co in oxidation states +2 versus +3. By systematically varying the Na2O/MoO3/B2O3 ratio, we tune relative populations of Co2+- and Co3+-bearing species in the flux. We monitor the competitive formation of intermediate phases - Na2MoO4, CoMoO4, Na2B4O7 and putative NaCoO2 - and show how these intermediates direct the ultimate borate phase. Moreover, by incrementally introducing NiO into the flux, we estimate solid solutions of the kotoite type (Co3-xNixB2O6) and ludwigite type (Co3-xNixBO5) and map their phase boundary in unprecedented detail. This compositional "switch" controls whether Co3+-rich borates are formed. We report the first synthesis of Co3-xNixB2O6 solid solutions within the range of 0 < x < 1, which has not been previously explored, revealing a magnetic ordering transition near 35 K. Crystals of Co2B2O5 (pyroborate) and Co3-xNixBO5 ludwigites have also been grown. Comprehensive structural refinements and magnetic measurements of all the phases are presented to substantiate our mechanistic insights.

The cubic Fe2-xMnxO3 is an intriguing material that has recently been investigated for various applications, including lithium-ion battery anodes, catalysts, energy storage media, humidity sensors, and photocatalysts. Despite its wide range of promising applications, the magnetic properties of Fe2-xMnxO3 remain controversial, with different sources reporting conflicting information regarding the type of magnetic ordering, phase transition temperature, and magnetic moment of this compound. This work presents a study of the magnetic state of three Fe2-xMnxO3:Ga solid solutions with varying Mn:Fe:Ga ratios, along with one gallium-free Fe2-xMnxO3 reference sample. We performed a detailed analysis of the actual chemical composition and crystal structure of the synthesized samples using energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS) to evaluate compositional differences. The magnetic states of the three Fe2-xMnxO3:Ga samples and the gallium-free Fe2-xMnxO3 were investigated using magnetometry and Mossbauer spectroscopy. The low-temperature magnetic anomalies were found to be more consistent with spin-glass-like freezing than with conventional long-range antiferromagnetic ordering. Although variations in magnetic behavior were observed and found to depend on composition and the cooling rate during synthesis, our results demonstrate that these factors do not account for the drastically different magnetic properties reported for similar bixbyite-type oxides. Instead, the apparent room-temperature ferrimagnetism observed in one sample is most likely extrinsic and can be attributed to a trace spinel-type impurity phase, as supported by magnetizations and ESR measurements. Thus, the origin of these discrepancies lies primarily in the chemical purity of the samples and, to a significant extent, in the synthesis technique employed.

A detailed study of the phase diagram of the Mn-Mg-B-O system is presented. The system exhibits significant diversity among phases of different structural types, including a number of Mg3−xMnxBO5 polytypes with the ludwigite, hulsite, takeuchiite and orthopinakiolite structures. The region of high magnesium concentration, comprising the polytype phases, was explored by the flux technique using a solvent based on Bi2Mo3O12-Na2O-B2O3. The way of stabilizing manganese 2+ and 3+ oxidation states via varying the Mn2O3/Na2O ratio was under study. Along with the Mg3−xMnxBO5 polytypes with the ludwigite, takeuchiite and orthopinakiolite structure, phases of Mg2−xMnxB2O5 pyroborate and Mg3−xMnxB2O6 kotoite, containing manganese only in the 2+ state, were also obtained. A new sodium-containing phase Mn6−xMgxNaB2O11 was discovered at high Na2O concentrations. The special role of sodium in this system indicated the necessity to consider the extended phase diagram of Mn-Mg-B-O-Na. The phase composition and structural parameters of the grown compounds were determined using the powder and single-crystal X-ray diffraction analysis. The comparable analysis of the magnetic properties of the obtained phases is presented.

For the first time, single crystals of Ni3_xMnxBO5:Cu, measuring up to 0.4x0.4x4 mm3, have been grown using the flux technique. The flux used was based on Bi2Mo3O12-B2O3; the addition of CuO served as a solvent component and promoted the growth of Ni3_xMnxBO5:Cu. Energy-dispersive X-ray spectroscopy (EDX) showed that the concentration of copper in the crystal, relative to the flux content was low-approximately 1:8. Subsequently, neutron diffraction, alternating current (AC) magnetization, and electron spin resonance (ESR) were performed on the Ni3_xMnxBO5:Cu compound, which is classified as ludwigite-type compound. Neutron diffraction results confirmed that the Ni3_xMnxBO5:Cu structure belongs to the Pbam space group. Furthermore, AC magnetization and ESR measurements identified three ferrimagnetic phase transitions occurring at 90 K, 95 K, and 150 K, as well as a canonical spin-glass transition near 50 K.

Single and polycrystalline samples of Mg2 – xMn1 + xBO5 (x = 0.0, 0.2, 0.4) oxyborates have been obtained for the first time by spontaneous crystallization from the solution–melt and through a solid-state reaction. X-ray diffraction studies have shown that compounds are crystallized with increasing manganese content in the ludwigite (space group Pbam)–hulsite (space group P2/m)–orthopinakiolite (space group Pbam) series and belong to the “3 Å wallpaper” borate family. A common property of materials is the presence of octahedral complexes (walls) consisting of manganese ions with a mixed valence at even crystallographic sites. The dc magnetization and specific heat of the Mg2 – xMn1 + xBO5 (x = 0.0, 0.2, 0.4) compounds have been studied for the first time. These studies have shown that cooling is accompanied by magnetic transitions, which are due to the ordering of several magnetic subsystems.

Ni2CrBO5 has been synthesized and investigated by X-ray diffraction, dc magnetization, and specific heat measurements. The unusual cation distribution has been established: the M1 and M3 sites are occupied by Ni2+ ions, the M2 site is by Cr3+ ions, and the M4 site is mixed, featuring both Ni2+ and Cr3+ ions. The magnetic order onsets at TN = 140 K, which is confirmed by a 7-type peak in specific heat, followed by the dome-shaped anomaly of the magnetization at about 30 K. In the magnetically ordered state, a remarkable sequence of temperature-induced magnetization reversal sensitive to the measurement's regime is observed. Dominant antiferromagnetic interactions are characterized by the Weiss temperature 0 = -73 K. The effective magnetic moment of 5.37 i B per formula unit is close to the spin-only one. The effect of the cation distribution on the magnetic properties is discussed.

Single crystals of Co2AlBO5 were synthesized using flux. The structural, magnetic, and electrical properties have been studied, with emphasis on cationic disorder effects. The Al3+ and Co2+ ions share four symmetry inequivalent sites. Large amplitudes of the displacement parameters for the M2 and M4 metal sites and the O4 oxygen site were found. The compound exhibits two magnetic transitions at T-1 = 41 K and T-2 = 20 K and shows a high crystallographic anisotropy. The random cationic distribution induces magnetic softness and an increase in electrical resistivity. The sources of the cationic disorder and the approach for controlling it are discussed.

With the type, size and quality of experimental samples playing a special role in searching for new materials, single crystal samples are of high value and methods of their fabrication have to be developed and constantly improved, to be adjusted to the peculiarities of an expected compound. The flux technique for producing chromium-containing materials is characterized by the low solubility of Cr2O3 used. The study deals with crystallization of Cr-containing borates HoCr3(BO3)4 with a huntite structure and oxyborates Cu2CrBO5 with a ludwigite structure in flux systems based on Li2WO4. Consideration is given not only to the possibility of growing sizable single crystals of these compounds, but also to a mixed huntite-ludwigite flux system intended to unify the growth technology and to identify the phase boundary of these compounds. The investigation of the phase diagram allowed the secondary phases to be found and analyzed. Powder and single crystal X-ray diffraction and element-sensitive EDX techniques were used to control the composition and structure of the obtained compounds. Orientational thermal and field dependences of magnetization of the obtained crystals HoCr3(BO3)4 and Cu2CrBO5 were measured.

GdFe 3 (BO 3 ) 4 , single crystals were grown from melt-solutions based on bismuth trimolybdate and lithium tungstate. Single crystals of gadolinium ferroborate from lithium-tungstate solution-melt were grown for the first time. The magnetic properties of the grown crystals are compared. It is shown that the GdFe 3 (BO 3 ) 4 , ferroborate obtained using bismuth solution-melt trimolybdate contains impurities of Bi 3+ ions (6% at.), which replace Gd 3+ ions. Whereas GdFe 3 (BO 3 ) 4 , ferroborate grown from a solution-melt based on lithium tungstate does not seem to contain such uncontrolled impurities. Keywords: crystal growth, antiferromagnets, multferroics.

The content of metal ions and their valence state for three Ni x Cu y Mn 3-x-y BO 5 compositions were estimated by EXAFS and XANES spectroscopy methods. In all three compositions, the copper y content did not exceed 0.25; in the third composition, some manganese ions entered the compound not only in the trivalent, but also in the divalent state. A detailed study of the magnetic properties showed that two magnetic transitions are observed in all compositions: one in the region of 60-75 K, and the second in the region of 10 K. Based on the exchange interactions calculated within the framework of the empirical model, the magnetic ordering temperatures for two- and three-lattice magnets were determined and it was assumed that the magnetic transition in the region of 60-75 K is associated with the ordering of magnetic moments in positions 2 and 3. Keywords: ludwigites, magnetic phase transition, indirect exchange interactions.

Co3Ge2O5(OH)4 relates to a specific group of 1:1 layered compounds with an ability to form either platy or tubular particles depending on chemical composition. Despite successful synthesis and perspective application, there is a lack of information on its crystal structure and magnetic properties, granted by Co ions. Co3Ge2O5(OH)4 phyllogermanate nanoparticles have been obtained using a hydrothermal method and characterised using powder X-ray diffraction and magnetisation measurements. Triclinic symmetry with a 1:P1 space group has been established. The unit cell contains three layers perpendicular to the c crystallographic direction, with 7.6 Å spacing and −b/3 shift of the middle layer. At a low magnetic field of 100 Oe the compound undergoes a magnetic transition at TN=5.2 K. The field of 9 T is not sufficient to take the sample to a magnetically saturated state with an asymptotic magnetic moment of 2.43 μB/Co2+. The estimations of the intralayer and interlayer exchange constants give values of J1/kB=2.75 K and J2/kB=0.25 K, respectively.

Multicomponent flux systems based on both Li2WO4-B2O3-Li2O-CuO-Cr2O3 and Bi2O3-MoO3-B2O3-Na2O-CuO-Cr2O3 were studied in order to grow Cu2CrBO5 crystals. The conditions for Cu2CrBO5 crystallization were investigated by varyingthe component ratios, and the peculiarities of their interaction were characterized by studying the formation sequence of high-temperature crystallizing phases. Special attention was paid to the problem of Cr2O3 solubility. Phase boundaries between CuCrO2, Cu2CrO4, and Cu2CrBO5 were considered. The crystal structure of the obtained samples was studied viasingle crystal and powder X-ray diffraction. The chemical composition of the grown crystals was examined using the EDX technique. Anactual ratio of Cu:Cr = 1.89:1.11 was found for Cu2CrBO5 grown from the lithium-tungstate system, which showed a small deviation from 2:1, implying the presence of a part of bivalent Cr2+ in the samples. Anomalies in the thermal dependence of magnetization were analyzed and compared with the previously obtained data for Cu2CrBO5. The anomaly at TC ≈ 42 K and the antiferromagnetic phase transition at TN ≈ 119 K were considered. Polarized Raman spectra of Cu2CrBO5 were obtained for the first time, and a comparative analysis of the obtained data with other monoclinic and orthorhombic ludwigites is presented. Along with the polarized room temperature spectra, the thermal evolution of Raman modes near the antiferromagnetic phase transition temperature TN ≈ 119 K is provided. The influence of the magnetic phase transition on the Raman spectra of Cu2CrBO5 is discussed.

The content of transition‐metal ions and their valence state for three compositions of NixCuyMn3−x−yBO5 are estimated by the methods of X‐ray absorption spectroscopy. In all the three compositions, the copper content does not exceed 0.25. One of the compositions has manganese ions both in the trivalent and bivalent states according to the K‐edge position. The calculations of the total energies of various cation‐ordered structures using the software package Wien2K show that copper ions predominately occupy one site, namely, 2(2d). The measurements of the magnetic properties show two types of magnetic transitions in all the three compositions, with one of them being in the range of 60–75 K and the other one at 10 K. Based on the exchange interactions calculated in the framework of the empirical model, magnetic ordering temperatures are estimated for two‐ and three‐sublattice structures and the magnetic transition in the range of 60–75 K is supposed to be connected with magnetic moment ordering in sites 2 and 3.

Cu 2 FeBO 5 ludwigite single crystals have been grown from a solution–melt by spontaneous crystallization. Using the X-ray diffraction method, the crystal structure has been resolved in detail. Cations in sites M2, M3, and M4 have turned out to be structurally disordered. It has been found that oxygen atoms are disordered in one of five nonequivalent sites (O4). As can be seen from Mössbauer spectroscopy data, Fe 3+ ions occupy four nonequivalent sites with different distortions of coordination octahedra. In the temperature range 40 K ≤ T ≤ 300 K, the spectra represent a superposition of quadrupole doublets. Static susceptibility measurements have revealed two magnetic features at T 1 = 35 K and T 2 = 20 K and spin-glass effects. Specific heat measurements in the interval 4–300 K have not discovered magnetic-transition-related anomalies.

Copper oxyborate single crystals with a ludwigite structure, Cu 2 MBO 5 (M = Cr, Fe, Mn), containing different substitutes in the trivalent subsystem have been grown from Bi 2 O 3 –MoO 3 –Na 2 O–B 2 O 3 fluxes. The structural properties of grown compounds have been compared in detail using X-ray diffraction and Raman spectroscopy methods. In addition, these methods have been used to determine the degree of cationic ordering in these ludwigites. The temperature and field dependences of the Cu 2 MBO 5 (M = Cr, Fe, Mn) ludwigite magnetization are presented.

A new multicationic structurally disordered K5FeHf(MoO4)6 crystal belonging to the molybdate family is synthesized by the two-stage solid state reaction method. The characterization of the electronic and vibrational properties of the K5FeHf(MoO4)6 was performed using density functional theory calculations, group theory, Raman and infrared spectroscopy. The vibrational spectra are dominated by vibrations of the MoO4 tetrahedra, while the lattice modes are observed in a low-wavenumber part of the spectra. The experimental gap in the phonon spectra between 450 and 700 cm−1 is in a good agreement with the simulated phonon density of the states. K5FeHf(MoO4)6 is a paramagnetic down to 4.2 K. The negative Curie–Weiss temperature of −6.7 K indicates dominant antiferromagnetic interactions in the compound. The direct and indirect optical bandgaps of K5FeHf(MoO4)6 are 2.97 and 3.21 eV, respectively. The K5FeHf(MoO4)6 bandgap narrowing, with respect to the variety of known molybdates and the ab initio calculations, is explained by the presence of Mott-Hubbard optical excitation in the system of Fe3+ ions.

To study the dependence of the properties of ternary oxides (Mn,Fe,Ga) 2 O 3 with the bixbyite structure on the composition, the temperature dependences of the magnetization and ac magnetic susceptibility of two single-crystal samples of different compositions obtained using the flux method were analyzed. A detailed study of the structure was carried out using single-crystal X-ray diffraction analysis, and the changes in structural parameters depending on the composition were analyzed. The dc magnetization and ac magnetic susceptibility of Fe 1.1 Mn 0.76 Ga 0.14 O 3 and Fe 0.65 Mn 1.1 Ga 0.26 O 3 bixbyites have been studied. Despite the qualitatively similar behavior of the magnetic properties, significant differences were also found, despite a small difference in the Mn/Fe/Ga ratio in the samples under study. It is shown that both compounds experience two successive low-temperature magnetic phase transitions from the paramagnetic phase at T=20-32 K as the temperature is lowered. Calculations of the Mydosh parameter for the detected phase transitions showed different degrees of ordering in the compounds under study. Keywords: transition metal oxides, magnetic phase transitions, spin glass state, bixbyite.