Vladimír Šepelák - Academia.edu (original) (raw)

Papers by Vladimír Šepelák

Over the past 20 years there has been a fairly extensive amount of work directed toward investiga... more Over the past 20 years there has been a fairly extensive amount of work directed toward investigation of mechanically induced metastable states formation in substances with close packed structure units. Among the most important contributions made in the 1980s by Russian scientists, the influence of the original structure on the nature of mechanically induced structural disordering in ferrites should be mentioned: if large cations are present in the system (e.g. in CdFe2O4, LaFeO3, DyFeO3, BiFeO3), the translation invariance completely disappears and amorphisation takes place. A characteristic feature of spinels containing relatively small cations (Zn, Ni, Co, Mg) is the possibility of preserving the long-range order at stressing (Boldyrev, 1994; Pavljukhin, 1987; Pavljukhin et al., 1984 a 1988; Rykov et al., 1989; Yermakov et al., 1982). A study of mechanically activated spinel ferrites has revealed that during energy-intensive milling they are transformed into an activated state wh...

Mechanochemická reakcia v spinelovom ferite Mechanicky indukované redukčné reakcie v tuhých látka... more Mechanochemická reakcia v spinelovom ferite Mechanicky indukované redukčné reakcie v tuhých látkach patria medzi významné mechanochemické procesy. V práci sú Mössbauerovou spektroskópiou, práškovou röntgenovou difrakciou a termickou analýzou študované zmeny vo ferite horčíka (MgFe 2 O 4), spôsobené jeho vysokoenergetickým mletím v oceľovom mlyne. Ferit horčíka patrí medzi mäkké magnetické materiály a nachádza množstvo aplikácií v heterogénnej katalýze a v magnetických technológiách. Štruktúrny vzorec feritu horčíka môže byť prezentovaný v tvare (Mg 1-x Fe x)[Mg x Fe 2-x ]O 4 , kde okrúhle zátvorky predstavujú tetraedrické (A) a hranaté zátvorky oktaedrické [B] kryštalografické polohy katiónov v tesne usporiadanej aniónovej podmriežke. Označenie x reprezentuje takzvaný stupeň inverzie, ktorý je určený koncentráciou Fe 3+ katiónov v tetraedrických polohách. Ferit horčíka je čiastočne inverzným spinelom (x = 0,91). Vysokoenergetický mlecí proces vedie k zmenšovaniu veľkosti kryštalitov feritu horčíka do nanometrickej oblasti (~ 10 nm). Tento efekt sa prejavuje vznikom superparamagnetických komponentov v Mössbauerových spektrách mletých vzoriek. Vysokoenergetické mletie feritu horčíka vedie okrem štruktúrnych zmien aj k jeho mechanochemickej redukcii. Produktmi mechanochemickej redukcie feritu horčíka sú tuhý roztok s wüstitovou štruktúrou (Mg 1-x Fe x O) a kovové železo (Fe). Množstvo reakčných produktov narastá s predlžujúcim sa časom mletia. Z kvantitatívnej analýzy Mössbauerových spektier vyplýva, že pomer Fe 2+ /(Fe 3+ +Fe 2+) narastá s predlžujúcim časom mletia z nulovej hodnoty (nemletá vzorka) na hodnotu 0,4 (vzorka mletá 20 minút). Produkty mechanochemickej redukcie sú štruktúrne a kompozične metastabilné. Oblasť teplotnej stability reakčných produktov je v práci určená štúdiom ich odozvy na zmenu teploty v dusíkovej atmosfére. Termická analýza nanokryštalických produktov mechanochemickej reakcie ukázala, že oblasť ich termickej stability je do 600 K. Pri teplotách nad 600 K dochádza k ich postupnej kryštalizácii, dokumentovanej zánikom superparamagnetických komponentov v Mössbauerových spektrách vyžíhaných vzoriek. Rast kryštalitov pri ohreve mletých vzoriek je sprevádzaný kompozičnými zmenami produktov mechanochemickej redukcie. Kovové železo sa postupne oxiduje zvyškovým kyslíkom, prítomným v dusíkovej atmosfére, na magnetit (Fe 3 O 4). Druhý produkt mechanochemickej redukcie, tuhý roztok Mg 1-x Fe x O, je pri ohreve v dusíkovej atmosfére relatívne stabilný.

Xii Latin american conference on the appLications of the mössbauer effect

Zeitschrift für Kristallographie - Crystalline Materials, 2017

In many cases, limitations in conventional synthesis routes hamper the accessibility to materials... more In many cases, limitations in conventional synthesis routes hamper the accessibility to materials with properties that have been predicted by theory. For instance, metastable compounds with local non-equilibrium structures can hardly be accessed by solid-state preparation techniques often requiring high synthesis temperatures. Also other ways of preparation lead to the thermodynamically stable rather than metastable products. Fortunately, such hurdles can be overcome by mechanochemical synthesis. Mechanical treatment of two or three starting materials in high-energy ball mills enables the synthesis of not only new, metastable compounds but also of nanocrystalline materials with unusual or enhanced properties such as ion transport. In this short review we report about local structures and ion transport of oxides and fluorides mechanochemically prepared by high-energy ball-milling.

Acta Montanistica Slovaca

Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders wer... more Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders were prepared via single -step mechanosynthesis performed at room temperature. The mechanically induced formation of a nanooxide product phase was followed by XRD, Fe-57 Mossbauer spectroscopy, and NMR. It is demonstrated that the mechanosynthesis of the complex oxide can proceed very rapidly (up to 4 h). This is i n a strong contrast to the conventio nal solid-state synthes is of the corn plex oxides, which req uires prolonged exposure at considerably elevated temperatures. It was revealed that the main structural features the mechanosynthesized oxides are nonequilibrium cation distribution and distorted oxygen polyhedra.

Xii Latin american conference on the appLications of the mössbauer effect

Zeitschrift für Kristallographie - Crystalline Materials, 2017

In many cases, limitations in conventional synthesis routes hamper the accessibility to materials... more In many cases, limitations in conventional synthesis routes hamper the accessibility to materials with properties that have been predicted by theory. For instance, metastable compounds with local non-equilibrium structures can hardly be accessed by solid-state preparation techniques often requiring high synthesis temperatures. Also other ways of preparation lead to the thermodynamically stable rather than metastable products. Fortunately, such hurdles can be overcome by mechanochemical synthesis. Mechanical treatment of two or three starting materials in high-energy ball mills enables the synthesis of not only new, metastable compounds but also of nanocrystalline materials with unusual or enhanced properties such as ion transport. In this short review we report about local structures and ion transport of oxides and fluorides mechanochemically prepared by high-energy ball-milling.

The Journal of Physical Chemistry C, 2013

Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilli... more Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilling and annealing of a titania−PTFE mixture. XPS, 19 F MAS NMR, FT-IR, Raman spectra, TEM and EDX analyses consistently indicated the oxidative decomposition of PTFE, inducing partial fluorination of titania. Incorporation of fluorine into titania was unambiguously confirmed by the appearance of a new XPS F1s peak at ∼685 eV, similar to those observed from TiOF 2. The intensity of the new F1s peak increased with comilling time and became a sole peak after milling for 3 h. At the same time, 19 F MAS NMR lines specific to PTFE disappeared. From these observations, we concluded that extensive decomposition of PTFE with simultaneous change in the chemical states of fluorine took place with the aid of titania. Upon annealing the comilled mixture in air, the amount of fluorine in the mixture decreased with increasing temperature, while the remaining fluorine migrated into the titania lattice, as confirmed by the decrease in the chemical shift of the 19 F MAS NMR lines and the decrease in the rutile (211) and (220) interplanar distances. These findings allow us to devise how to control the amount, states, and spatial distribution of the fluorine incorporated into titania.

Acta Montanistica Slovaca

Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders wer... more Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders were prepared via single -step mechanosynthesis performed at room temperature. The mechanically induced formation of a nanooxide product phase was followed by XRD, Fe-57 Mossbauer spectroscopy, and NMR. It is demonstrated that the mechanosynthesis of the complex oxide can proceed very rapidly (up to 4 h). This is i n a strong contrast to the conventio nal solid-state synthes is of the corn plex oxides, which req uires prolonged exposure at considerably elevated temperatures. It was revealed that the main structural features the mechanosynthesized oxides are nonequilibrium cation distribution and distorted oxygen polyhedra.

The Journal of Physical Chemistry C, 2013

Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilli... more Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilling and annealing of a titania−PTFE mixture. XPS, 19 F MAS NMR, FT-IR, Raman spectra, TEM and EDX analyses consistently indicated the oxidative decomposition of PTFE, inducing partial fluorination of titania. Incorporation of fluorine into titania was unambiguously confirmed by the appearance of a new XPS F1s peak at ∼685 eV, similar to those observed from TiOF 2. The intensity of the new F1s peak increased with comilling time and became a sole peak after milling for 3 h. At the same time, 19 F MAS NMR lines specific to PTFE disappeared. From these observations, we concluded that extensive decomposition of PTFE with simultaneous change in the chemical states of fluorine took place with the aid of titania. Upon annealing the comilled mixture in air, the amount of fluorine in the mixture decreased with increasing temperature, while the remaining fluorine migrated into the titania lattice, as confirmed by the decrease in the chemical shift of the 19 F MAS NMR lines and the decrease in the rutile (211) and (220) interplanar distances. These findings allow us to devise how to control the amount, states, and spatial distribution of the fluorine incorporated into titania.

Journal of Solid State Chemistry, 2011

A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical p... more A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical processing of Bi 2 O 3 /Ga 2 O 3 /Al 2 O 3 mixtures and subsequent annealing, was investigated by XRD, EDX, and 27 Al MAS NMR. The structure of the Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi 2 (Ga x Al 1 À x) 4 O 9 series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the 27 Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi 2 (Ga x Al 1 À x) 4 O 9. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.

Journal of Solid State Chemistry, 2011

A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical p... more A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical processing of Bi 2 O 3 /Ga 2 O 3 /Al 2 O 3 mixtures and subsequent annealing, was investigated by XRD, EDX, and 27 Al MAS NMR. The structure of the Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi 2 (Ga x Al 1 À x) 4 O 9 series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the 27 Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi 2 (Ga x Al 1 À x) 4 O 9. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.

Hyperfine Interactions, 2012

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by ... more Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mössbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization

Zeitschrift für Physikalische Chemie

For the first time, a spinel-type high entropy oxide (Zn0.25Cu0.25Mg0.25Co0.25)Al2O4 as well as i... more For the first time, a spinel-type high entropy oxide (Zn0.25Cu0.25Mg0.25Co0.25)Al2O4 as well as its derivative lithiated high entropy oxyfluoride Li0.5(Zn0.25Cu0.25Mg0.25Co0.25)0.5Al2O3.5F0.5 and oxychloride Li0.5(Zn0.25Cu0.25Mg0.25Co0.25)0.5Al2O3.5Cl0.5 are prepared in the nanostructured state via high-energy co-milling of the simple oxide precursors and the halides (LiF or LiCl) as sources of lithium, fluorine and chlorine. Their nanostructure is investigated by XRD, HR-TEM, EDX and XPS spectroscopy. It is revealed that incorporation of lithium into the structure of spinel oxide together with the anionic substitution has significant effect on its short-range order, size and morphology of crystallites as well as on its oxidation/reduction processes. The charge capacity of the as-prepared nanomaterials tested by cyclic voltammetry is found to be rather poor despite lithiation of the samples in comparison to previously reported spinel-type high entropy oxides. Nevertheless, the prese...

Journal of Physics and Chemistry of Solids

Journal of the American Ceramic Society

Starting from gelatinous aluminum chloride hydroxide, the transformation process towards α-Al 2 O... more Starting from gelatinous aluminum chloride hydroxide, the transformation process towards α-Al 2 O 3 was examined by using 27 Al NMR, both in the liquid and solid states, as a main analytical tool. By increasing the hydrolysis ratio (h, defined as [OH − ]/[Al 3+ ]) of the starting aqueous precursor up to h = 2.5, the transition temperature to the final product, α-Al 2 O 3 , decreased to as low as 500 °C. In this case, the structural change from amorphous alumina to α-Al 2 O 3 took place without intermediate transition Al 2 O 3 phases.

Journal of Materials Science

Over the past 20 years there has been a fairly extensive amount of work directed toward investiga... more Over the past 20 years there has been a fairly extensive amount of work directed toward investigation of mechanically induced metastable states formation in substances with close packed structure units. Among the most important contributions made in the 1980s by Russian scientists, the influence of the original structure on the nature of mechanically induced structural disordering in ferrites should be mentioned: if large cations are present in the system (e.g. in CdFe2O4, LaFeO3, DyFeO3, BiFeO3), the translation invariance completely disappears and amorphisation takes place. A characteristic feature of spinels containing relatively small cations (Zn, Ni, Co, Mg) is the possibility of preserving the long-range order at stressing (Boldyrev, 1994; Pavljukhin, 1987; Pavljukhin et al., 1984 a 1988; Rykov et al., 1989; Yermakov et al., 1982). A study of mechanically activated spinel ferrites has revealed that during energy-intensive milling they are transformed into an activated state wh...

Mechanochemická reakcia v spinelovom ferite Mechanicky indukované redukčné reakcie v tuhých látka... more Mechanochemická reakcia v spinelovom ferite Mechanicky indukované redukčné reakcie v tuhých látkach patria medzi významné mechanochemické procesy. V práci sú Mössbauerovou spektroskópiou, práškovou röntgenovou difrakciou a termickou analýzou študované zmeny vo ferite horčíka (MgFe 2 O 4), spôsobené jeho vysokoenergetickým mletím v oceľovom mlyne. Ferit horčíka patrí medzi mäkké magnetické materiály a nachádza množstvo aplikácií v heterogénnej katalýze a v magnetických technológiách. Štruktúrny vzorec feritu horčíka môže byť prezentovaný v tvare (Mg 1-x Fe x)[Mg x Fe 2-x ]O 4 , kde okrúhle zátvorky predstavujú tetraedrické (A) a hranaté zátvorky oktaedrické [B] kryštalografické polohy katiónov v tesne usporiadanej aniónovej podmriežke. Označenie x reprezentuje takzvaný stupeň inverzie, ktorý je určený koncentráciou Fe 3+ katiónov v tetraedrických polohách. Ferit horčíka je čiastočne inverzným spinelom (x = 0,91). Vysokoenergetický mlecí proces vedie k zmenšovaniu veľkosti kryštalitov feritu horčíka do nanometrickej oblasti (~ 10 nm). Tento efekt sa prejavuje vznikom superparamagnetických komponentov v Mössbauerových spektrách mletých vzoriek. Vysokoenergetické mletie feritu horčíka vedie okrem štruktúrnych zmien aj k jeho mechanochemickej redukcii. Produktmi mechanochemickej redukcie feritu horčíka sú tuhý roztok s wüstitovou štruktúrou (Mg 1-x Fe x O) a kovové železo (Fe). Množstvo reakčných produktov narastá s predlžujúcim sa časom mletia. Z kvantitatívnej analýzy Mössbauerových spektier vyplýva, že pomer Fe 2+ /(Fe 3+ +Fe 2+) narastá s predlžujúcim časom mletia z nulovej hodnoty (nemletá vzorka) na hodnotu 0,4 (vzorka mletá 20 minút). Produkty mechanochemickej redukcie sú štruktúrne a kompozične metastabilné. Oblasť teplotnej stability reakčných produktov je v práci určená štúdiom ich odozvy na zmenu teploty v dusíkovej atmosfére. Termická analýza nanokryštalických produktov mechanochemickej reakcie ukázala, že oblasť ich termickej stability je do 600 K. Pri teplotách nad 600 K dochádza k ich postupnej kryštalizácii, dokumentovanej zánikom superparamagnetických komponentov v Mössbauerových spektrách vyžíhaných vzoriek. Rast kryštalitov pri ohreve mletých vzoriek je sprevádzaný kompozičnými zmenami produktov mechanochemickej redukcie. Kovové železo sa postupne oxiduje zvyškovým kyslíkom, prítomným v dusíkovej atmosfére, na magnetit (Fe 3 O 4). Druhý produkt mechanochemickej redukcie, tuhý roztok Mg 1-x Fe x O, je pri ohreve v dusíkovej atmosfére relatívne stabilný.

Xii Latin american conference on the appLications of the mössbauer effect

Zeitschrift für Kristallographie - Crystalline Materials, 2017

In many cases, limitations in conventional synthesis routes hamper the accessibility to materials... more In many cases, limitations in conventional synthesis routes hamper the accessibility to materials with properties that have been predicted by theory. For instance, metastable compounds with local non-equilibrium structures can hardly be accessed by solid-state preparation techniques often requiring high synthesis temperatures. Also other ways of preparation lead to the thermodynamically stable rather than metastable products. Fortunately, such hurdles can be overcome by mechanochemical synthesis. Mechanical treatment of two or three starting materials in high-energy ball mills enables the synthesis of not only new, metastable compounds but also of nanocrystalline materials with unusual or enhanced properties such as ion transport. In this short review we report about local structures and ion transport of oxides and fluorides mechanochemically prepared by high-energy ball-milling.

Acta Montanistica Slovaca

Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders wer... more Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders were prepared via single -step mechanosynthesis performed at room temperature. The mechanically induced formation of a nanooxide product phase was followed by XRD, Fe-57 Mossbauer spectroscopy, and NMR. It is demonstrated that the mechanosynthesis of the complex oxide can proceed very rapidly (up to 4 h). This is i n a strong contrast to the conventio nal solid-state synthes is of the corn plex oxides, which req uires prolonged exposure at considerably elevated temperatures. It was revealed that the main structural features the mechanosynthesized oxides are nonequilibrium cation distribution and distorted oxygen polyhedra.

Xii Latin american conference on the appLications of the mössbauer effect

Zeitschrift für Kristallographie - Crystalline Materials, 2017

In many cases, limitations in conventional synthesis routes hamper the accessibility to materials... more In many cases, limitations in conventional synthesis routes hamper the accessibility to materials with properties that have been predicted by theory. For instance, metastable compounds with local non-equilibrium structures can hardly be accessed by solid-state preparation techniques often requiring high synthesis temperatures. Also other ways of preparation lead to the thermodynamically stable rather than metastable products. Fortunately, such hurdles can be overcome by mechanochemical synthesis. Mechanical treatment of two or three starting materials in high-energy ball mills enables the synthesis of not only new, metastable compounds but also of nanocrystalline materials with unusual or enhanced properties such as ion transport. In this short review we report about local structures and ion transport of oxides and fluorides mechanochemically prepared by high-energy ball-milling.

The Journal of Physical Chemistry C, 2013

Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilli... more Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilling and annealing of a titania−PTFE mixture. XPS, 19 F MAS NMR, FT-IR, Raman spectra, TEM and EDX analyses consistently indicated the oxidative decomposition of PTFE, inducing partial fluorination of titania. Incorporation of fluorine into titania was unambiguously confirmed by the appearance of a new XPS F1s peak at ∼685 eV, similar to those observed from TiOF 2. The intensity of the new F1s peak increased with comilling time and became a sole peak after milling for 3 h. At the same time, 19 F MAS NMR lines specific to PTFE disappeared. From these observations, we concluded that extensive decomposition of PTFE with simultaneous change in the chemical states of fluorine took place with the aid of titania. Upon annealing the comilled mixture in air, the amount of fluorine in the mixture decreased with increasing temperature, while the remaining fluorine migrated into the titania lattice, as confirmed by the decrease in the chemical shift of the 19 F MAS NMR lines and the decrease in the rutile (211) and (220) interplanar distances. These findings allow us to devise how to control the amount, states, and spatial distribution of the fluorine incorporated into titania.

Acta Montanistica Slovaca

Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders wer... more Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders were prepared via single -step mechanosynthesis performed at room temperature. The mechanically induced formation of a nanooxide product phase was followed by XRD, Fe-57 Mossbauer spectroscopy, and NMR. It is demonstrated that the mechanosynthesis of the complex oxide can proceed very rapidly (up to 4 h). This is i n a strong contrast to the conventio nal solid-state synthes is of the corn plex oxides, which req uires prolonged exposure at considerably elevated temperatures. It was revealed that the main structural features the mechanosynthesized oxides are nonequilibrium cation distribution and distorted oxygen polyhedra.

The Journal of Physical Chemistry C, 2013

Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilli... more Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilling and annealing of a titania−PTFE mixture. XPS, 19 F MAS NMR, FT-IR, Raman spectra, TEM and EDX analyses consistently indicated the oxidative decomposition of PTFE, inducing partial fluorination of titania. Incorporation of fluorine into titania was unambiguously confirmed by the appearance of a new XPS F1s peak at ∼685 eV, similar to those observed from TiOF 2. The intensity of the new F1s peak increased with comilling time and became a sole peak after milling for 3 h. At the same time, 19 F MAS NMR lines specific to PTFE disappeared. From these observations, we concluded that extensive decomposition of PTFE with simultaneous change in the chemical states of fluorine took place with the aid of titania. Upon annealing the comilled mixture in air, the amount of fluorine in the mixture decreased with increasing temperature, while the remaining fluorine migrated into the titania lattice, as confirmed by the decrease in the chemical shift of the 19 F MAS NMR lines and the decrease in the rutile (211) and (220) interplanar distances. These findings allow us to devise how to control the amount, states, and spatial distribution of the fluorine incorporated into titania.

Journal of Solid State Chemistry, 2011

A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical p... more A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical processing of Bi 2 O 3 /Ga 2 O 3 /Al 2 O 3 mixtures and subsequent annealing, was investigated by XRD, EDX, and 27 Al MAS NMR. The structure of the Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi 2 (Ga x Al 1 À x) 4 O 9 series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the 27 Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi 2 (Ga x Al 1 À x) 4 O 9. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.

Journal of Solid State Chemistry, 2011

A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical p... more A series of Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions (0 r x r 1), prepared by mechanochemical processing of Bi 2 O 3 /Ga 2 O 3 /Al 2 O 3 mixtures and subsequent annealing, was investigated by XRD, EDX, and 27 Al MAS NMR. The structure of the Bi 2 (Ga x Al 1 À x) 4 O 9 solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi 2 (Ga x Al 1 À x) 4 O 9 series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the 27 Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi 2 (Ga x Al 1 À x) 4 O 9. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.

Hyperfine Interactions, 2012

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by ... more Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mössbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization

Zeitschrift für Physikalische Chemie

For the first time, a spinel-type high entropy oxide (Zn0.25Cu0.25Mg0.25Co0.25)Al2O4 as well as i... more For the first time, a spinel-type high entropy oxide (Zn0.25Cu0.25Mg0.25Co0.25)Al2O4 as well as its derivative lithiated high entropy oxyfluoride Li0.5(Zn0.25Cu0.25Mg0.25Co0.25)0.5Al2O3.5F0.5 and oxychloride Li0.5(Zn0.25Cu0.25Mg0.25Co0.25)0.5Al2O3.5Cl0.5 are prepared in the nanostructured state via high-energy co-milling of the simple oxide precursors and the halides (LiF or LiCl) as sources of lithium, fluorine and chlorine. Their nanostructure is investigated by XRD, HR-TEM, EDX and XPS spectroscopy. It is revealed that incorporation of lithium into the structure of spinel oxide together with the anionic substitution has significant effect on its short-range order, size and morphology of crystallites as well as on its oxidation/reduction processes. The charge capacity of the as-prepared nanomaterials tested by cyclic voltammetry is found to be rather poor despite lithiation of the samples in comparison to previously reported spinel-type high entropy oxides. Nevertheless, the prese...

Journal of Physics and Chemistry of Solids

Journal of the American Ceramic Society

Starting from gelatinous aluminum chloride hydroxide, the transformation process towards α-Al 2 O... more Starting from gelatinous aluminum chloride hydroxide, the transformation process towards α-Al 2 O 3 was examined by using 27 Al NMR, both in the liquid and solid states, as a main analytical tool. By increasing the hydrolysis ratio (h, defined as [OH − ]/[Al 3+ ]) of the starting aqueous precursor up to h = 2.5, the transition temperature to the final product, α-Al 2 O 3 , decreased to as low as 500 °C. In this case, the structural change from amorphous alumina to α-Al 2 O 3 took place without intermediate transition Al 2 O 3 phases.

Journal of Materials Science