Radostina Stoyanova | Bulgarian Academy of Sciences (original) (raw)

Papers by Radostina Stoyanova

Batteries

Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical applicati... more Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical application by combining the Co substitution and MgO treatment strategies. The oxides are prepared via solid-state reactions at 900 °C. The structure, morphology, and oxidation state of transition metal ions for Co-substituted and MgO-treated oxides are carefully examined via X-ray diffraction, IR and Raman spectroscopies, FESEM with EDX, specific surface area measurement, and XPS spectroscopy. The ability of oxides to store sodium reversibly is analyzed within a temperature range of 10 to 50 °C via CV experiments, galvanostatic measurements, and EIS, using half and full sodium ion cells. The changes in the local structure and oxidation state of transition metal ions during Na+ intercalation are monitored via operando XAS experiments. It is found that the Co substituents have a positive impact on the rate capability of layered oxides, while Mg additives lead to a strong increase in the capacity a...

Materials

After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerg... more After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerging in the market. This is a result of the concerns regarding sustainability and production costs of the former, as well as issues related to safety and toxicity. Electrode materials for the new sodium-ion batteries may contain available and sustainable elements such as sodium itself, as well as iron or manganese, while eliminating the common cobalt cathode compounds and copper anode current collectors for lithium-ion batteries. The multiple oxidation states, abundance, and availability of manganese favor its use, as it was shown early on for primary batteries. Regarding structural considerations, an extraordinarily successful group of cathode materials are layered oxides of sodium, and transition metals, with manganese being the major component. However, other technologies point towards Prussian blue analogs, NASICON-related phosphates, and fluorophosphates. The role of manganese in the...

Journal of The Electrochemical Society, Dec 1, 1995

ABSTRACT

Materials

Sodium iron phosphate-pyrophosphate, Na4Fe3(PO4)2P2O7 (NFPP) emerges as an excellent cathode mate... more Sodium iron phosphate-pyrophosphate, Na4Fe3(PO4)2P2O7 (NFPP) emerges as an excellent cathode material for sodium-ion batteries. Because of lower electronic conductivity, its electrochemical performance depends drastically on the synthesis method. Herein, we provide a simple and unified method for synthesis of composites between NFPP and reduced graphene oxide (rGO) and standard carbon black, designed as electrode materials for both sodium- and lithium-ion batteries. The carbon additives affect only the morphology and textural properties of the composites. The performance of composites in sodium and lithium cells is evaluated at elevated temperatures. It is found that NFPP/rGO outperforms NFPP/C in both Na and Li storage due to its hybrid mechanism of energy storage. In sodium half-cells, NFPP/rGO delivers a reversible capacity of 95 mAh/g at 20 °C and 115 mAh/g at 40 °C with a cycling stability of 95% and 88% at a rate of C/2. In lithium half-cells, the capacity reaches a value of 1...

Journal of Solid State Electrochemistry, Apr 7, 1999

Energy Storage Materials, Jun 1, 2022

Meeting abstracts, 2010

ABSTRACT Tin-containing nanometric and amorphous intermetallics and alloys are envisaged as negat... more ABSTRACT Tin-containing nanometric and amorphous intermetallics and alloys are envisaged as negative electrodes for high-capacity lithium ion batteries. Nanocrystalline FeSn2 has been prepared by reduction of Sn2+ and Fe3+ in tetraethylene glycol at 185 °C. Microcrystalline FeSn2 has been prepared at 490 °C. The properties of nano-FeSn2 and micro-FeSn2 have been observed to be very different. The small particles size hinders the long-range magnetism and consequently the Mössbauer spectra are modified. The nanocrystalline particles of FeSn2 show exothermal effects in the DTA experiment that are not observed in the micrometric particles. Nanocrystalline FeSn2 exhibits a much better electrochemical behavior and electrode stability than microcrystalline FeSn2.

The launch of the first commercial lithium-ion battery by Sony at 1990 has promoted intense resea... more The launch of the first commercial lithium-ion battery by Sony at 1990 has promoted intense research interest in layered LiNi1-yCoyO2 solid solutions [1–3]. The interest in these oxides is not only practical, but also theoretical, aimed at understanding the electronic structure of oxo-bridged mixed valence Ni2+-Ni3+ pairs.

Materials Today: Proceedings, 2022

Materials

To make supercapattery devices feasible, there is an urgent need to find electrode materials that... more To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li2Mn(SO4)2 and orthorhombic Li2Mn2(SO4)3, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20–60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperatur...

RSC Advances, 2015

The study demonstrates unusual capabilities of phospho-olivine NaMnPO4 to intercalate lithium and... more The study demonstrates unusual capabilities of phospho-olivine NaMnPO4 to intercalate lithium and sodium reversibly, which makes it attractive electrode material instead of the conventional lithium analogue LiMnPO4.

Molecules

The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and... more The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and salinomycinic acids (HL) with metal ions of type M4+ and the known antiproliferative potential of antibiotics has provoked our interest in exploring the coordination processes between MonH/SalH and ions of Ce4+. (1) Methods: Novel monensinate and salinomycinate cerium(IV)-based complexes were synthesized and structurally characterized by elemental analysis, a plethora of physicochemical methods, density functional theory, molecular dynamics, and biological assays. (2) Results: The formation of coordination species of a general composition [CeL2(OH)2] and [CeL(NO3)2(OH)], depending on reaction conditions, was proven both experimentally and theoretically. The metal(IV) complexes [CeL(NO3)2(OH)] possess promising cytotoxic activity against the human tumor uterine cervix (HeLa) cell line, being highly selective (non-tumor embryo Lep-3 vs. HeLa) compared to cisplatin, oxaliplatin, and epirub...

Batteries

The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode ... more The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode materials with a desired rate capability. Herein, we provide an in-depth examination of the Li-storage performance of sodium titanate nanowires as negative electrodes in hybrid Li,Na-ion batteries. Titanate nanowires were prepared by a simple and reproducible hydrothermal method. At a low reaction pressure, the well-isolated nanowires are formed, while by increasing the reaction pressure from 2 to 30 bar, the isolated nanowires tend to bundle. In nanowires, the local coordinations of Na and Ti atoms deviate from those in Na2Ti3O7 and Na2Ti6O13 and slightly depend on the reaction pressure. During the annealing at 350 °C, both Na and Ti coordinations undergo further changes. The nanowires are highly defective, and they easily crystallize into Na2Ti6O13 and Na2Ti3O7 phases. The lithium storage properties are evaluated in lithium-ion cells vs. lithium metal anode and titanate electrodes fabr...

Journal of Molecular Structure, 2017

Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characteri... more Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characterized. The photophysical properties of the new compounds have been investigated in organic solvents of different polarity. It has been shown that both compounds are solvent depended. Cu(II) and Zn(II) complexes of NI2 were obtained and characterized by IR-NMR, fluorescence and EPR spectroscopy. The influence of different metal cations on the fluorescence intensity has been investigated in acetonitrile solution. Antimicrobial composite PLA-metal complexes materials have been obtained for the first time. Microbiological activity of both metal complexes has been investigated in vitro against different Gram-positive and Gram-negative bacteria and two yeasts. The various antimicrobial activities and the minimum inhibitory concentrations (MICs) of both complexes have been determined. The microbiological activity of composite materials PLA-metal complexes in thin polymeric film has also been investigated. The results suggest that the new metal complexes could find application in designing new antimicrobial preparations to control the spread of infections.

Batteries

Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries tha... more Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migrat...

Journal of Alloys and Compounds, 2015

ABSTRACT Abstract A nanocomposite of sodium titanate/titania nanotrees self-organized in a parall... more ABSTRACT Abstract A nanocomposite of sodium titanate/titania nanotrees self-organized in a parallel fashion to form nanoforests is successfully prepared and used as high-performance anode for Na-ion microbatteries. The first step of the synthesis is the anodic oxidation of Ti foils to form self-organized amorphous TiO2 nanotubes followed by insertion of sodium in aqueous media at room temperature. Then the composite is thermally dehydrated and crystallized as monoclinic Na2Ti6O13/rutile nanotrees. EPR spectra evidence a significant increase in Ti3+ content during sodium/proton insertion and a decrease on heating. SEM images reveal that while the height of the nanotubes is similar to the nanoforest (c.a. 8.0 μm) the morphology changes from aligned nanotubes to nanotrees of complex texture. The electrochemical results of sodium test cells in non-aqueous electrolyte using the Na2Ti6O13/TiO2 nanocomposite electrodes show flat profiles of sodium insertion and de-insertion at 0.7 and 0.9 V, respectively. The observed reversible capacity of 130 μA h cm−2 over 150 cycles is almost threefold the value of titania nanotubes annealed at a same temperature. Both characteristics are of great interest to achieve safe and efficient Na-ion microbatteries.

Journal of Solid State Chemistry, 2017

The present contribution provides new structural and spectroscopic data on the formation of solid... more The present contribution provides new structural and spectroscopic data on the formation of solid solutions between hydrated and dehydrated sulfate salts of sodium-nickel and sodium-manganese in a whole concentration range: Na 2 Ni 1-x Mn x (SO 4) 2 •yH 2 O, 0 d x d 1.0. Using powder XRD, electron paramagnetic resonance spectroscopy (EPR), IR and Raman spectroscopy it has been found that double sodium-nickel and sodium-manganese salts form solid solutions Na 2 Ni 1x Mn x (SO 4) 2 •4H 2 O with a blödite-type of structure within a broad concentration range of 0 d x d 0.49, while the manganese rich compositions Na 2 Ni 1-x Mn x (SO 4) 2 •2H 2 O (0.97 d x d 1.0) crystallize in the kröhnkite-type of structure. The Ni-based blödites Na 2 Ni 1-x Mn x (SO 4) 2 •4H 2 O dehydrate between 140 and 260 o C into anhydrous salts Na 2 Ni 1-x Mn x (SO 4) 2 , 0 d x d 0.44, with a structure where Ni 1-x Mn x O 6 octahedra are bridged into pairs by edge-and corner sharing SO 4 2groups. Both TEM and EPR methods show that the Ni 2+ and Mn 2+ ions are homogenously distributed over three crystallographic positions of the large monoclinic cell. The dehydration of the kröhnkite phase Na 2 Ni 1-x Mn x (SO 4) 2 •2H 2 O yields the alluaudite phase Na 2+G Mn 2-G/2 (SO 4) 3 , where the Na-to-Mn ratio decreases and all Ni 2+ dopants are released from the structure. The process of the dehydration is discussed in terms of structural aspects taking into account the distortion degree of the Ni,MnO 6 and SO 4 polyhedra.

Batteries

Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical applicati... more Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical application by combining the Co substitution and MgO treatment strategies. The oxides are prepared via solid-state reactions at 900 °C. The structure, morphology, and oxidation state of transition metal ions for Co-substituted and MgO-treated oxides are carefully examined via X-ray diffraction, IR and Raman spectroscopies, FESEM with EDX, specific surface area measurement, and XPS spectroscopy. The ability of oxides to store sodium reversibly is analyzed within a temperature range of 10 to 50 °C via CV experiments, galvanostatic measurements, and EIS, using half and full sodium ion cells. The changes in the local structure and oxidation state of transition metal ions during Na+ intercalation are monitored via operando XAS experiments. It is found that the Co substituents have a positive impact on the rate capability of layered oxides, while Mg additives lead to a strong increase in the capacity a...

Materials

After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerg... more After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerging in the market. This is a result of the concerns regarding sustainability and production costs of the former, as well as issues related to safety and toxicity. Electrode materials for the new sodium-ion batteries may contain available and sustainable elements such as sodium itself, as well as iron or manganese, while eliminating the common cobalt cathode compounds and copper anode current collectors for lithium-ion batteries. The multiple oxidation states, abundance, and availability of manganese favor its use, as it was shown early on for primary batteries. Regarding structural considerations, an extraordinarily successful group of cathode materials are layered oxides of sodium, and transition metals, with manganese being the major component. However, other technologies point towards Prussian blue analogs, NASICON-related phosphates, and fluorophosphates. The role of manganese in the...

Journal of The Electrochemical Society, Dec 1, 1995

ABSTRACT

Materials

Sodium iron phosphate-pyrophosphate, Na4Fe3(PO4)2P2O7 (NFPP) emerges as an excellent cathode mate... more Sodium iron phosphate-pyrophosphate, Na4Fe3(PO4)2P2O7 (NFPP) emerges as an excellent cathode material for sodium-ion batteries. Because of lower electronic conductivity, its electrochemical performance depends drastically on the synthesis method. Herein, we provide a simple and unified method for synthesis of composites between NFPP and reduced graphene oxide (rGO) and standard carbon black, designed as electrode materials for both sodium- and lithium-ion batteries. The carbon additives affect only the morphology and textural properties of the composites. The performance of composites in sodium and lithium cells is evaluated at elevated temperatures. It is found that NFPP/rGO outperforms NFPP/C in both Na and Li storage due to its hybrid mechanism of energy storage. In sodium half-cells, NFPP/rGO delivers a reversible capacity of 95 mAh/g at 20 °C and 115 mAh/g at 40 °C with a cycling stability of 95% and 88% at a rate of C/2. In lithium half-cells, the capacity reaches a value of 1...

Journal of Solid State Electrochemistry, Apr 7, 1999

Energy Storage Materials, Jun 1, 2022

Meeting abstracts, 2010

ABSTRACT Tin-containing nanometric and amorphous intermetallics and alloys are envisaged as negat... more ABSTRACT Tin-containing nanometric and amorphous intermetallics and alloys are envisaged as negative electrodes for high-capacity lithium ion batteries. Nanocrystalline FeSn2 has been prepared by reduction of Sn2+ and Fe3+ in tetraethylene glycol at 185 °C. Microcrystalline FeSn2 has been prepared at 490 °C. The properties of nano-FeSn2 and micro-FeSn2 have been observed to be very different. The small particles size hinders the long-range magnetism and consequently the Mössbauer spectra are modified. The nanocrystalline particles of FeSn2 show exothermal effects in the DTA experiment that are not observed in the micrometric particles. Nanocrystalline FeSn2 exhibits a much better electrochemical behavior and electrode stability than microcrystalline FeSn2.

The launch of the first commercial lithium-ion battery by Sony at 1990 has promoted intense resea... more The launch of the first commercial lithium-ion battery by Sony at 1990 has promoted intense research interest in layered LiNi1-yCoyO2 solid solutions [1–3]. The interest in these oxides is not only practical, but also theoretical, aimed at understanding the electronic structure of oxo-bridged mixed valence Ni2+-Ni3+ pairs.

Materials Today: Proceedings, 2022

Materials

To make supercapattery devices feasible, there is an urgent need to find electrode materials that... more To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li2Mn(SO4)2 and orthorhombic Li2Mn2(SO4)3, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20–60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperatur...

RSC Advances, 2015

The study demonstrates unusual capabilities of phospho-olivine NaMnPO4 to intercalate lithium and... more The study demonstrates unusual capabilities of phospho-olivine NaMnPO4 to intercalate lithium and sodium reversibly, which makes it attractive electrode material instead of the conventional lithium analogue LiMnPO4.

Molecules

The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and... more The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and salinomycinic acids (HL) with metal ions of type M4+ and the known antiproliferative potential of antibiotics has provoked our interest in exploring the coordination processes between MonH/SalH and ions of Ce4+. (1) Methods: Novel monensinate and salinomycinate cerium(IV)-based complexes were synthesized and structurally characterized by elemental analysis, a plethora of physicochemical methods, density functional theory, molecular dynamics, and biological assays. (2) Results: The formation of coordination species of a general composition [CeL2(OH)2] and [CeL(NO3)2(OH)], depending on reaction conditions, was proven both experimentally and theoretically. The metal(IV) complexes [CeL(NO3)2(OH)] possess promising cytotoxic activity against the human tumor uterine cervix (HeLa) cell line, being highly selective (non-tumor embryo Lep-3 vs. HeLa) compared to cisplatin, oxaliplatin, and epirub...

Batteries

The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode ... more The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode materials with a desired rate capability. Herein, we provide an in-depth examination of the Li-storage performance of sodium titanate nanowires as negative electrodes in hybrid Li,Na-ion batteries. Titanate nanowires were prepared by a simple and reproducible hydrothermal method. At a low reaction pressure, the well-isolated nanowires are formed, while by increasing the reaction pressure from 2 to 30 bar, the isolated nanowires tend to bundle. In nanowires, the local coordinations of Na and Ti atoms deviate from those in Na2Ti3O7 and Na2Ti6O13 and slightly depend on the reaction pressure. During the annealing at 350 °C, both Na and Ti coordinations undergo further changes. The nanowires are highly defective, and they easily crystallize into Na2Ti6O13 and Na2Ti3O7 phases. The lithium storage properties are evaluated in lithium-ion cells vs. lithium metal anode and titanate electrodes fabr...

Journal of Molecular Structure, 2017

Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characteri... more Abstract Two new 1,8-naphthalimide derivatives (NI1 and NI2) have been synthesized and characterized. The photophysical properties of the new compounds have been investigated in organic solvents of different polarity. It has been shown that both compounds are solvent depended. Cu(II) and Zn(II) complexes of NI2 were obtained and characterized by IR-NMR, fluorescence and EPR spectroscopy. The influence of different metal cations on the fluorescence intensity has been investigated in acetonitrile solution. Antimicrobial composite PLA-metal complexes materials have been obtained for the first time. Microbiological activity of both metal complexes has been investigated in vitro against different Gram-positive and Gram-negative bacteria and two yeasts. The various antimicrobial activities and the minimum inhibitory concentrations (MICs) of both complexes have been determined. The microbiological activity of composite materials PLA-metal complexes in thin polymeric film has also been investigated. The results suggest that the new metal complexes could find application in designing new antimicrobial preparations to control the spread of infections.

Batteries

Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries tha... more Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migrat...

Journal of Alloys and Compounds, 2015

ABSTRACT Abstract A nanocomposite of sodium titanate/titania nanotrees self-organized in a parall... more ABSTRACT Abstract A nanocomposite of sodium titanate/titania nanotrees self-organized in a parallel fashion to form nanoforests is successfully prepared and used as high-performance anode for Na-ion microbatteries. The first step of the synthesis is the anodic oxidation of Ti foils to form self-organized amorphous TiO2 nanotubes followed by insertion of sodium in aqueous media at room temperature. Then the composite is thermally dehydrated and crystallized as monoclinic Na2Ti6O13/rutile nanotrees. EPR spectra evidence a significant increase in Ti3+ content during sodium/proton insertion and a decrease on heating. SEM images reveal that while the height of the nanotubes is similar to the nanoforest (c.a. 8.0 μm) the morphology changes from aligned nanotubes to nanotrees of complex texture. The electrochemical results of sodium test cells in non-aqueous electrolyte using the Na2Ti6O13/TiO2 nanocomposite electrodes show flat profiles of sodium insertion and de-insertion at 0.7 and 0.9 V, respectively. The observed reversible capacity of 130 μA h cm−2 over 150 cycles is almost threefold the value of titania nanotubes annealed at a same temperature. Both characteristics are of great interest to achieve safe and efficient Na-ion microbatteries.

Journal of Solid State Chemistry, 2017

The present contribution provides new structural and spectroscopic data on the formation of solid... more The present contribution provides new structural and spectroscopic data on the formation of solid solutions between hydrated and dehydrated sulfate salts of sodium-nickel and sodium-manganese in a whole concentration range: Na 2 Ni 1-x Mn x (SO 4) 2 •yH 2 O, 0 d x d 1.0. Using powder XRD, electron paramagnetic resonance spectroscopy (EPR), IR and Raman spectroscopy it has been found that double sodium-nickel and sodium-manganese salts form solid solutions Na 2 Ni 1x Mn x (SO 4) 2 •4H 2 O with a blödite-type of structure within a broad concentration range of 0 d x d 0.49, while the manganese rich compositions Na 2 Ni 1-x Mn x (SO 4) 2 •2H 2 O (0.97 d x d 1.0) crystallize in the kröhnkite-type of structure. The Ni-based blödites Na 2 Ni 1-x Mn x (SO 4) 2 •4H 2 O dehydrate between 140 and 260 o C into anhydrous salts Na 2 Ni 1-x Mn x (SO 4) 2 , 0 d x d 0.44, with a structure where Ni 1-x Mn x O 6 octahedra are bridged into pairs by edge-and corner sharing SO 4 2groups. Both TEM and EPR methods show that the Ni 2+ and Mn 2+ ions are homogenously distributed over three crystallographic positions of the large monoclinic cell. The dehydration of the kröhnkite phase Na 2 Ni 1-x Mn x (SO 4) 2 •2H 2 O yields the alluaudite phase Na 2+G Mn 2-G/2 (SO 4) 3 , where the Na-to-Mn ratio decreases and all Ni 2+ dopants are released from the structure. The process of the dehydration is discussed in terms of structural aspects taking into account the distortion degree of the Ni,MnO 6 and SO 4 polyhedra.