Susana García-martín | Universidad Complutense de Madrid (original) (raw)
Papers by Susana García-martín
IMAPS other content, Sep 1, 2013
The ordering of cations within the perovskite structure can have a profound effect on the physica... more The ordering of cations within the perovskite structure can have a profound effect on the physical properties. A number of AA′BB′O6 perovskite phases which have both a rock salt ordering of the B/B′ cations and a layered ordering of the A/A′ cations have recently been prepared and studied. In some of these compositions complex nanoscale superstructure formation has been observed. These superstructures are the result of compositional modulations involving the occupancies of the A and A′ cations and are accompanied by a twinning of the octahedral tilt system. A wide variety of patterns are observed, such as 1-dimensional stripes or 2-dimensional chessboards which can have periodicities which are either commensurate or incommensurate with the underlying subcell. These superstructures cannot be easily detected by powder X-ray diffraction but have been observed using a combination of high resolution transmission electron microscopy, electron diffraction, and neutron powder diffraction. The factors which determine the dimensionality and periodicity of the superstructures are discussed and compared with the closely related Li based perovskite systems.
Journal of the American Chemical Society, Nov 3, 2021
Complex compositional and displacive modulations of the crystal structure of KLaMnWO6 are imaged ... more Complex compositional and displacive modulations of the crystal structure of KLaMnWO6 are imaged with atomic resolution by means of scanning transmission electron microscopy (STEM). This oxide is stabilized by cation vacancies leading to a La1+x/3K1-xMnWO6 stoichiometry. Compositional modulation on both the K and La layers are revealed in the high-angle annular dark-field STEM (HAADF-STEM) images. The compositional modulation within the La layer is coupled with the modulation of the octahedral tilting, which is exposed by imaging of the anion sublattice in annular bright-field STEM (ABF-STEM) images. These complex modulations are accommodated in a 5√2ap × 5√2ap × 2ap perovskite-type structure.
ChemInform, Jan 26, 1988
The pyrochlore-type title materials are prepared by heating stoichiometric mixtures of KNO3, WO3,... more The pyrochlore-type title materials are prepared by heating stoichiometric mixtures of KNO3, WO3, and M2O5 (M: Nb, Ta) in a porcelain crucible at 900 rc C (12 h). From an analysis of their dehydration kinetics, studied by thermogravimetry, a diffusion echanism is proposed, which follows the structural model previously described in the literature.
Journal of the American Chemical Society, Oct 21, 2008
Transmission electron microscopy studies of the perovskite NaLaMgWO 6 reveal the formation of a c... more Transmission electron microscopy studies of the perovskite NaLaMgWO 6 reveal the formation of a complex, compositionally modulated structure. Annular dark field scanning transmission electron microscopy images and scanning transmission electron microscopy-electron energy-loss spectroscopy scans show that this modulation involves a repeating pattern of La-rich and La-poor stripes, each stripe 6 a p or approximately 24 A wide (where a p is the edge length of the simple cubic perovskite unit cell). High-resolution transmission electron microscopy images clearly show, and electron diffraction patterns confirm, a periodicity of 12 a p along either the [100] p or [010] p direction. Available evidence suggests a spontaneous separation into stripes that possess the nominal stoichiometry, NaLaMgWO 6, alternating with Na-poor/La-rich stripes that have a stoichiometry of (La x Na 1-3 x )LaMgWO 6. X-ray powder diffraction measurements are insensitive to this intricate structural complexity, which may be a more widespread feature of (A (+)Ln (3+))MM'O 6 perovskites than previously appreciated.
Optics and Laser Technology, 2024
Inorganic Chemistry, Dec 4, 2018
Fe 13.5 2.22+ (AsO 4−x) 8 (OH) 6 , x = 0.25, was prepared using the reaction of iron metal with a... more Fe 13.5 2.22+ (AsO 4−x) 8 (OH) 6 , x = 0.25, was prepared using the reaction of iron metal with arsenate in aqueous solution and autogenous pressure. Its crystal structure reveals a dumortierite-like framework with mixed-valent Fe 2+/ Fe 3+ in double chains creating channel walls. Remarkably, hexagonal channels consist of chains of face-sharing Fe 2+ O 6 octahedra, 3/4th occupied, whereas AsO 4 tetrahedra occupy triangular ones with a single "up" orientation according to the polar P6 3 mc symmetry. We have analyzed the transformation of this phase upon heating, in which several chemical processes interact, including dehydroxylation, arsenate to arsenite reduction, and oxidative exsolution of a significant part of iron (ca. 15%) found at the surface as hematite and amorphous Fe-rich surficial layer. It leaves a strongly disordered composite structure between several Fe 3+-based subunits, in which ∼80% of them is ordered in a complex supercell. Because of the high degree of disorder, the crystal chemistry of the individual subunits and their plausible imbrication were considered to unravel the most plausible ideal 3D model.
Optical Materials, Jul 1, 2022
Inorganic Chemistry, May 19, 2021
The antiferromagnetic behavior of Fe 3+ oxides of composition RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 , RE ... more The antiferromagnetic behavior of Fe 3+ oxides of composition RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 , RE 2.2 Ba 3.2 Ca 2.6 Fe 8 O 21 , and RE-Ba 2 Ca 2 Fe 5 O 13 (RE = Gd, Tb) is highly influenced by the type of oxygen polyhedron around the Fe 3+ cations and their ordering, which is coupled with the layered RE/Ba/Ca arrangement within the perovskite-related structure. Determination of the magnetic structures reveals different magnetic moments associated with Fe 3+ spins in the different oxygen polyhedra (octahedron, tetrahedron, and square pyramid). The structural aspects impact on the strength of the Fe-O-Fe superexchange interactions and, therefore, on the Neél temperature (T N) of the compounds. The oxides present an interesting transition from three-dimensional (3D) to two-dimensional (2D) magnetic behavior above T N. The 2D magnetic interactions are stronger within the FeO6 octahedra layers than in the FeO4 tetrahedra layers.
Journal of Alloys and Compounds, Oct 1, 2019
Ln 3 Ni 2 RuO 9 (Ln ¼ La, Nd) oxides (prepared by a solid state metathesis route) adopt a monocli... more Ln 3 Ni 2 RuO 9 (Ln ¼ La, Nd) oxides (prepared by a solid state metathesis route) adopt a monoclinic (P2 1 /n) A 2 BB'O 6 double perovskite structure wherein the two independent octahedral 2c and 2d sites are occupied by Ni 2þ and (Ni 2þ 1/3 Ru 5þ 2/3) cations, respectively. In contrast to the expected ferromagnetic behavior, Ln 3 Ni 2 RuO 9 oxides show a spin glass behavior without long range magnetic order down to 2 K. These results reveal the importance of competing nearest neighbor (NN), next nearest neighbor (NNN) and third nearest neighbor (third NN) interactions between the magnetic Ni 2þ and Ru 5þ ions in the partially ordered double perovskite structure that conspire to thwart the expected ferromagnetic order in these materials.
Journal of Materials Science, 1991
On the basis of the distances AX and B-X, in the defect pyrochlores A2B206, a general approach to... more On the basis of the distances AX and B-X, in the defect pyrochlores A2B206, a general approach to the coordination polyhedra around A and B metal ions is established. Results show that, depending on these distances, coordination of 3 + 3 and 3 + 3 + 3 around A ions can be found and that a region of low stability should exist.
Inorganic Chemistry, Oct 9, 2019
Solid State Ionics, Dec 1, 1989
ABSTRACT
Journal of Solid State Chemistry, Nov 1, 1999
The microstructure of samples of di4erent composition belonging to the cation-de5cient La 1/3؊x L... more The microstructure of samples of di4erent composition belonging to the cation-de5cient La 1/3؊x Li 3x NbO 3 , 04x40.06, solid solution has been studied by selected area electron di4raction and high resolution transmission electron microscopy. The materials show a perovskite-related structure with basic lattice parameters a&'2a p , b&'2a p , c&2a p. Besides, short-range cation ordering gives place to a larger unit cell of dimensions a&3.5'2a p , b&'2a p , c&4a p. The lithium-containing compunds also present a complex microdomain structure of the octahedra tilting framework.
Physical Review B, Jan 12, 2015
The magnetism of the oxygen deficient, A-site layered perovskite TbBaMn 2 O 5.75 has been studied... more The magnetism of the oxygen deficient, A-site layered perovskite TbBaMn 2 O 5.75 has been studied by magnetic susceptibility vs. temperature measurements and neutron powder diffraction. Four magnetic phases have been identified. Above 457 K a charge melted state exists where ferromagnetic double exchange interactions between the Mn ions dominate. Below 457 K charge ordering occurs and the exchange interactions become primarily antiferromagnetic. The magnetic moment in this phase is too large to be consistent with a charge ordering of Mn 3+ and Mn 4+ but could be explained by having 2 e g electrons being shared among 3 Mn centers, causing them to act as a single paramagnetic unit. This suggests that S = 11/2 (Mn 3.33+) 3 polaron trimers may be present along with Mn 3+. Below 203 K long range ordering of the moments on the Mn ions occurs. Neutron powder diffraction data at 52 K reveal a magnetic structure containing an ↑↑↑↓ pattern of spins which is consistent with the formation of tripolarons. Below 11 K the Tb 3+ ions also undergo long range magnetic ordering.
Inorganic Chemistry, Dec 19, 2022
ChemInform, Aug 23, 2010
-Several LnSr2Ta2Li7O12 compounds are prepared as ordered tetragonal garnet phase along with a sm... more -Several LnSr2Ta2Li7O12 compounds are prepared as ordered tetragonal garnet phase along with a small amount of cubic garnet by firing stoichiometric amounts of the metal oxides and a 20% excess of Li 2CO3 (pre-reacted pellets on ZrO2 in Al2O3 crucible, 850 C, 14 h). The presence of a small amount of cubic garnet is correlated with partial Li and some degree of H + /Li + exchange. The tetragonal garnet structure implies cation ordering has to be present to prevent short Li-Li interactions in order to accommodate seven Li ions. AC impedance measurements at >150 C on pellets sintered at 1000 C for 2 h (70-80% of theoretical density) show the highest conductivity for the Ln: Pr system with 1.5 x 10-5 S/cm which is in line with other tetragonal garnet systems; the Li ion conductivity being low due to the ordered Li distribution.-(HOWARD, M. A.;
Journal of Solid State Chemistry, Jun 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2016
IMAPS other content, Sep 1, 2013
The ordering of cations within the perovskite structure can have a profound effect on the physica... more The ordering of cations within the perovskite structure can have a profound effect on the physical properties. A number of AA′BB′O6 perovskite phases which have both a rock salt ordering of the B/B′ cations and a layered ordering of the A/A′ cations have recently been prepared and studied. In some of these compositions complex nanoscale superstructure formation has been observed. These superstructures are the result of compositional modulations involving the occupancies of the A and A′ cations and are accompanied by a twinning of the octahedral tilt system. A wide variety of patterns are observed, such as 1-dimensional stripes or 2-dimensional chessboards which can have periodicities which are either commensurate or incommensurate with the underlying subcell. These superstructures cannot be easily detected by powder X-ray diffraction but have been observed using a combination of high resolution transmission electron microscopy, electron diffraction, and neutron powder diffraction. The factors which determine the dimensionality and periodicity of the superstructures are discussed and compared with the closely related Li based perovskite systems.
Journal of the American Chemical Society, Nov 3, 2021
Complex compositional and displacive modulations of the crystal structure of KLaMnWO6 are imaged ... more Complex compositional and displacive modulations of the crystal structure of KLaMnWO6 are imaged with atomic resolution by means of scanning transmission electron microscopy (STEM). This oxide is stabilized by cation vacancies leading to a La1+x/3K1-xMnWO6 stoichiometry. Compositional modulation on both the K and La layers are revealed in the high-angle annular dark-field STEM (HAADF-STEM) images. The compositional modulation within the La layer is coupled with the modulation of the octahedral tilting, which is exposed by imaging of the anion sublattice in annular bright-field STEM (ABF-STEM) images. These complex modulations are accommodated in a 5√2ap × 5√2ap × 2ap perovskite-type structure.
ChemInform, Jan 26, 1988
The pyrochlore-type title materials are prepared by heating stoichiometric mixtures of KNO3, WO3,... more The pyrochlore-type title materials are prepared by heating stoichiometric mixtures of KNO3, WO3, and M2O5 (M: Nb, Ta) in a porcelain crucible at 900 rc C (12 h). From an analysis of their dehydration kinetics, studied by thermogravimetry, a diffusion echanism is proposed, which follows the structural model previously described in the literature.
Journal of the American Chemical Society, Oct 21, 2008
Transmission electron microscopy studies of the perovskite NaLaMgWO 6 reveal the formation of a c... more Transmission electron microscopy studies of the perovskite NaLaMgWO 6 reveal the formation of a complex, compositionally modulated structure. Annular dark field scanning transmission electron microscopy images and scanning transmission electron microscopy-electron energy-loss spectroscopy scans show that this modulation involves a repeating pattern of La-rich and La-poor stripes, each stripe 6 a p or approximately 24 A wide (where a p is the edge length of the simple cubic perovskite unit cell). High-resolution transmission electron microscopy images clearly show, and electron diffraction patterns confirm, a periodicity of 12 a p along either the [100] p or [010] p direction. Available evidence suggests a spontaneous separation into stripes that possess the nominal stoichiometry, NaLaMgWO 6, alternating with Na-poor/La-rich stripes that have a stoichiometry of (La x Na 1-3 x )LaMgWO 6. X-ray powder diffraction measurements are insensitive to this intricate structural complexity, which may be a more widespread feature of (A (+)Ln (3+))MM&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;O 6 perovskites than previously appreciated.
Optics and Laser Technology, 2024
Inorganic Chemistry, Dec 4, 2018
Fe 13.5 2.22+ (AsO 4−x) 8 (OH) 6 , x = 0.25, was prepared using the reaction of iron metal with a... more Fe 13.5 2.22+ (AsO 4−x) 8 (OH) 6 , x = 0.25, was prepared using the reaction of iron metal with arsenate in aqueous solution and autogenous pressure. Its crystal structure reveals a dumortierite-like framework with mixed-valent Fe 2+/ Fe 3+ in double chains creating channel walls. Remarkably, hexagonal channels consist of chains of face-sharing Fe 2+ O 6 octahedra, 3/4th occupied, whereas AsO 4 tetrahedra occupy triangular ones with a single "up" orientation according to the polar P6 3 mc symmetry. We have analyzed the transformation of this phase upon heating, in which several chemical processes interact, including dehydroxylation, arsenate to arsenite reduction, and oxidative exsolution of a significant part of iron (ca. 15%) found at the surface as hematite and amorphous Fe-rich surficial layer. It leaves a strongly disordered composite structure between several Fe 3+-based subunits, in which ∼80% of them is ordered in a complex supercell. Because of the high degree of disorder, the crystal chemistry of the individual subunits and their plausible imbrication were considered to unravel the most plausible ideal 3D model.
Optical Materials, Jul 1, 2022
Inorganic Chemistry, May 19, 2021
The antiferromagnetic behavior of Fe 3+ oxides of composition RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 , RE ... more The antiferromagnetic behavior of Fe 3+ oxides of composition RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 , RE 2.2 Ba 3.2 Ca 2.6 Fe 8 O 21 , and RE-Ba 2 Ca 2 Fe 5 O 13 (RE = Gd, Tb) is highly influenced by the type of oxygen polyhedron around the Fe 3+ cations and their ordering, which is coupled with the layered RE/Ba/Ca arrangement within the perovskite-related structure. Determination of the magnetic structures reveals different magnetic moments associated with Fe 3+ spins in the different oxygen polyhedra (octahedron, tetrahedron, and square pyramid). The structural aspects impact on the strength of the Fe-O-Fe superexchange interactions and, therefore, on the Neél temperature (T N) of the compounds. The oxides present an interesting transition from three-dimensional (3D) to two-dimensional (2D) magnetic behavior above T N. The 2D magnetic interactions are stronger within the FeO6 octahedra layers than in the FeO4 tetrahedra layers.
Journal of Alloys and Compounds, Oct 1, 2019
Ln 3 Ni 2 RuO 9 (Ln ¼ La, Nd) oxides (prepared by a solid state metathesis route) adopt a monocli... more Ln 3 Ni 2 RuO 9 (Ln ¼ La, Nd) oxides (prepared by a solid state metathesis route) adopt a monoclinic (P2 1 /n) A 2 BB'O 6 double perovskite structure wherein the two independent octahedral 2c and 2d sites are occupied by Ni 2þ and (Ni 2þ 1/3 Ru 5þ 2/3) cations, respectively. In contrast to the expected ferromagnetic behavior, Ln 3 Ni 2 RuO 9 oxides show a spin glass behavior without long range magnetic order down to 2 K. These results reveal the importance of competing nearest neighbor (NN), next nearest neighbor (NNN) and third nearest neighbor (third NN) interactions between the magnetic Ni 2þ and Ru 5þ ions in the partially ordered double perovskite structure that conspire to thwart the expected ferromagnetic order in these materials.
Journal of Materials Science, 1991
On the basis of the distances AX and B-X, in the defect pyrochlores A2B206, a general approach to... more On the basis of the distances AX and B-X, in the defect pyrochlores A2B206, a general approach to the coordination polyhedra around A and B metal ions is established. Results show that, depending on these distances, coordination of 3 + 3 and 3 + 3 + 3 around A ions can be found and that a region of low stability should exist.
Inorganic Chemistry, Oct 9, 2019
Solid State Ionics, Dec 1, 1989
ABSTRACT
Journal of Solid State Chemistry, Nov 1, 1999
The microstructure of samples of di4erent composition belonging to the cation-de5cient La 1/3؊x L... more The microstructure of samples of di4erent composition belonging to the cation-de5cient La 1/3؊x Li 3x NbO 3 , 04x40.06, solid solution has been studied by selected area electron di4raction and high resolution transmission electron microscopy. The materials show a perovskite-related structure with basic lattice parameters a&'2a p , b&'2a p , c&2a p. Besides, short-range cation ordering gives place to a larger unit cell of dimensions a&3.5'2a p , b&'2a p , c&4a p. The lithium-containing compunds also present a complex microdomain structure of the octahedra tilting framework.
Physical Review B, Jan 12, 2015
The magnetism of the oxygen deficient, A-site layered perovskite TbBaMn 2 O 5.75 has been studied... more The magnetism of the oxygen deficient, A-site layered perovskite TbBaMn 2 O 5.75 has been studied by magnetic susceptibility vs. temperature measurements and neutron powder diffraction. Four magnetic phases have been identified. Above 457 K a charge melted state exists where ferromagnetic double exchange interactions between the Mn ions dominate. Below 457 K charge ordering occurs and the exchange interactions become primarily antiferromagnetic. The magnetic moment in this phase is too large to be consistent with a charge ordering of Mn 3+ and Mn 4+ but could be explained by having 2 e g electrons being shared among 3 Mn centers, causing them to act as a single paramagnetic unit. This suggests that S = 11/2 (Mn 3.33+) 3 polaron trimers may be present along with Mn 3+. Below 203 K long range ordering of the moments on the Mn ions occurs. Neutron powder diffraction data at 52 K reveal a magnetic structure containing an ↑↑↑↓ pattern of spins which is consistent with the formation of tripolarons. Below 11 K the Tb 3+ ions also undergo long range magnetic ordering.
Inorganic Chemistry, Dec 19, 2022
ChemInform, Aug 23, 2010
-Several LnSr2Ta2Li7O12 compounds are prepared as ordered tetragonal garnet phase along with a sm... more -Several LnSr2Ta2Li7O12 compounds are prepared as ordered tetragonal garnet phase along with a small amount of cubic garnet by firing stoichiometric amounts of the metal oxides and a 20% excess of Li 2CO3 (pre-reacted pellets on ZrO2 in Al2O3 crucible, 850 C, 14 h). The presence of a small amount of cubic garnet is correlated with partial Li and some degree of H + /Li + exchange. The tetragonal garnet structure implies cation ordering has to be present to prevent short Li-Li interactions in order to accommodate seven Li ions. AC impedance measurements at >150 C on pellets sintered at 1000 C for 2 h (70-80% of theoretical density) show the highest conductivity for the Ln: Pr system with 1.5 x 10-5 S/cm which is in line with other tetragonal garnet systems; the Li ion conductivity being low due to the ordered Li distribution.-(HOWARD, M. A.;
Journal of Solid State Chemistry, Jun 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2016