The diffusion coefficient of Li$^+$ ions ($D_{\rm Li}$) in the battery material Li$_x$CoO$_2$ has... more The diffusion coefficient of Li$^+$ ions ($D_{\rm Li}$) in the battery material Li$_x$CoO$_2$ has been investigated by muon-spin relaxation ($\mu^+$SR). Based on the experiments in zero-field and weak longitudinal-fields at temperatures up to 400 K, we determined the fluctuation rate ($\nu$) of the fields on the muons due to their interaction with the nuclear moments. Combined with susceptibility data and
Magnetism of a misfit layered cobaltite (Ca2Co4/3Cu2/3O4)RSx (CoO2) (x ∼ 0.62, RS denotes a rocks... more Magnetism of a misfit layered cobaltite (Ca2Co4/3Cu2/3O4)RSx (CoO2) (x ∼ 0.62, RS denotes a rocksalt-type block) was investigated by a positive muon spin rotation and relaxation (µ+SR) experiment. A transition to an incommensurate (IC) spin density wave (SDW) state was found below 180 K (= T on C ); and a clear oscillation due to a static internal magnetic field was observed below 140 K (= TC). Furthermore, an anisotropic behavior of the zero-field µ+SR experiment indicated that the IC-SDW propagates in the a-b plane, with oscillating moments directed along the c axis. These results were quite similar to those for the related compound (Ca2CoO3)RS0.62(CoO2), i.e., Ca3Co4O9. Since the IC-SDW field in (Ca2Co4/3Cu2/3O4)RS0.62(CoO2) was approximately same to those in pure and doped (Ca2CoO3)RS0.62(CoO2), it was concluded that the IC- SDW exist in the (CoO2) planes.
The magnetic nature of a novel one-dimensional compound NaCr2O4 with zigzag CrO2 chains has been ... more The magnetic nature of a novel one-dimensional compound NaCr2O4 with zigzag CrO2 chains has been studied by muon spin rotation and relaxation (μ+SR) and neutron diffraction (ND). It is found that NaCr2O4 undergoes an antiferromagnetic transition at TN = 125 K, below which the Cr moments in each zigzag chain align ferromagnetically along the c-axis but antifer- romagnetically along the a-axis between adjacent zigzag chains. For the solid solution system Ca1−xNaxCr2O4, μ+SR measurements reveal the evolution of a complex magnetic order with increasing Ca content (1 − x), which finally enters into an incommensurate AF ordered state below TN = 21 for CaCr2O4.
In order to elucidate the dependence of the magnetic ground state on the Ca content (x) in Sr1−xC... more In order to elucidate the dependence of the magnetic ground state on the Ca content (x) in Sr1−xCaxCo2P2 (0 ≤ x ≤ 1, ThCr2Si2-type structure), we have performed muon spin rotation and relaxation (μ+SR) experiments on Sr1−xCaxCo2P2 powder samples mainly in a zero applied field. The end member compound, SrCo2P2, is found to be paramagnetic down to 19 mK. As x increases, such a paramagnetic ground state is observed down to 1.8 K until x = 0.45. Then, as x increases further, a short-range antiferromagnetic (AF) ordered phase appears at low temperatures for 0.48 ≤ x ≤ 0.75, and finally, a long-range AF ordered phase is stabilized for x > 0.75. The internal magnetic field of the other end member compound, CaCo2P2, is well consistent with that of the A-type AF order state, which was proposed from neutron scattering experiments. The phase diagram determined with μ+SR is different from that proposed by macroscopic measurements. For an isostructural compound, LaCo2P2, static magnetic order...
(http://www.tytlabs.com/review/issue/rcw.cgi?file=462_029sugiyama.pdf&PASS=1) In this paper, we w... more (http://www.tytlabs.com/review/issue/rcw.cgi?file=462_029sugiyama.pdf&PASS=1) In this paper, we will give an introduction to the method itself but also summary of our muon spin relaxation work on Li-diffusion in battery positive electrode materials. Furthermore, we will show that the method is not limited to studying only Li-diffusion but can also be extended to other physical and/or electrochemical properties in lithium transition-metal oxides.
In order to investigate the microscopic magnetic nature of a sodium phospho-olivine, we have meas... more In order to investigate the microscopic magnetic nature of a sodium phospho-olivine, we have measured μ+SR spectra for NaxFePO4 using a powder sample in the temperature range between 2 and 500 K. ZF-μ+SR measurements below 200 K at TRIUMF showed the appearance of static magnetic order below TN= 61 K, where the susceptibility-vs.-temperature curve exhibits a sharp maximum due to an antiferromagnetic (AF) transition. The wide distribution found for the internal magnetic field (Hint) was explained by the formation of AF order with the spread in Hint due to random distribution of Na vacancies. At higher temperatures, the ZF-spectrum for Na0.7FePO4, obtained at J-PARC, is found to change from a low-T static behavior to a high-T dynamic behavior above 300 K. This is consistent with the fact that Na+ ions are reversibly extracted from and intercalated into the NaxFePO4 lattice, while there is no NMR study on Na-diffusion in NaxFePO4 due to large Fe moments.
In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-$\... more In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-$\mu^+$SR spectra for the Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ powder samples with $x=0$, 0.2, 0.4, 0.5, 0.6, 0.8, and 1. Due to a characteristic time window and spatial resolution of $\mu^+$SR, the obtained phase diagram was found to be rather different from that determined by magnetization measurements. That is, as $x$ increases from 0, a Pauli-paramagnetic phase is observed even at the lowest $T$ measured (1.8~K) until $x=0.4$, then, a spin-glass like phase appears at $0.5\leq x\leq0.6$, and then, a phase with wide field distribution probably due to incommensurate AF order is detected for $x=0.8$, and finally, a commensurate $A$-type AF ordered phase (for $x=1$) is stabilized below $T_{\rm N}\sim80~$K. Such change is most likely reasonable and connected to the shrink of the $c$-axis length with $x$, which naturally enhances the magnetic interaction between the two adjacent Co planes.
Thanks to the unique power of muon-spin spectroscopy, we found that the quasi-one-dimensional Co-... more Thanks to the unique power of muon-spin spectroscopy, we found that the quasi-one-dimensional Co-Rh oxides An+2CoRhnO3n+3 (A = Ca, Sr; n=1, 2, and 3) exhibit a two-dimensional antiferromagnetic transition that ranges from TN^on=185 K for n=1 to 125 K for n=3 with a transition width (deltaT) of about 80 K. The variation of TN^on with n is explained by the increase in the distance between the neighboring CoRhnO3n+3 chains. Static magnetic order is observed below the endpoint of TN (=TN^on-deltaT) for each of the three samples. The existence of the two-frequency components in the ZF-spectrum indicates the appearance of ferrimagnetic order for Ca3CoRhO6 below 20 K.
Proceedings ICT'03. 22nd International Conference on Thermoelectrics (IEEE Cat. No.03TH8726), 2003
ABSTRACT Magnetism of misfit layered cobaltites, [Ca2CoO3]0.62RS[CoO2] and [Ca2Co43/Cu23/O4]0.62R... more ABSTRACT Magnetism of misfit layered cobaltites, [Ca2CoO3]0.62RS[CoO2] and [Ca2Co43/Cu23/O4]0.62RS[CoO2] (RS denotes a rocksalt-type block), was investigated by a positive muon spin rotation and relaxation (μ+SR) experiment. For the former cobaltite, a transition to an incommensurate (IC) spin density wave (SDW) state was found below 100 K (=TSDWon) and a clear oscillation due to a static internal magnetic field was observed below 30 K (=TSDW). For the latter cobaltite, TSDWon=180 K and TSDW=140 K, respectively. The wide transition width (= 40-70 K) suggested that a short-range IC-SDW order appeared below TSDWon and a long-range order completed below TSDW. Furthermore, an anisotropic behavior of the zero-field μ+SR spectra on the c axis aligned samples indicated that the IC-SDW propagates in the a-b plane, with oscillating moments directed along the c axis. These results suggest that the IC-SDW exist not in the rocksalt-type block but in the CoO2 plane.
Proceedings ICT'03. 22nd International Conference on Thermoelectrics (IEEE Cat. No.03TH8726), 2003
ABSTRACT In order to apply layered cobaltites to thermoelectric (TE) devices, we need aligned cer... more ABSTRACT In order to apply layered cobaltites to thermoelectric (TE) devices, we need aligned ceramics to exploit their superior in-plane TE properties. Here, we report the preparation and characterization of c-axis aligned [Ca2CoO3]0.62[CoO2] (CCO) ceramics by the reactive templated grain growth (RTGG) method. As reactive templates, we synthesized platelike β-Co(OH)2 particles by a precipitation method. The template particles were mixed with a complementary reactant, CaCO3, and aligned by a tape-casting. Upon heat treatment, they reacted to form a CCO ceramic with almost perfectly c-alignment (Lotgering's orientation degree, f > 0.99). The highly textured ceramic shows significantly large in-plane electrical conductivity (σab): i.e., the value of σab was 2.61 × 104 S/m at 1060 K, where the value is around 60 % of that of a single crystal. We conclude that the RTGG method must be an effective and versatile technique for the preparation of large-sized TE materials with high TE performances.
In order to clarify the reason why the hydrogen desorption temperature (Td) of MgH2 is lowered by... more In order to clarify the reason why the hydrogen desorption temperature (Td) of MgH2 is lowered by milling, we have studied the change in a local nuclear magnetic field with temperature by means of μ+SR. We have found a very clear oscillation in the ZF-spectrum at 2 K for the "milled" and "milled with Nb2O5" samples, while such oscillation is weaker for the "as-prepared" MgH2. It was also found that the oscillation signal is stable up to 250 K and is assigned mainly due to the formation of a Hμ+H system. At temperatures above ambient T, we also found that the ZF-μ+SR spectrum exhibits a static Kubo-Toyabe behavior due to the nuclear magnetic field of 1H. Furthermore, it was clarified that rapid H diffusion starts well below Td only in the milled samples, leading to the conclusion that the consequent enhanced diffusion rate in MgH2 is essential to accelerate the desorption reaction and to decrease Td.
The diffusion coefficient of Li$^+$ ions ($D_{\rm Li}$) in the battery material Li$_x$CoO$_2$ has... more The diffusion coefficient of Li$^+$ ions ($D_{\rm Li}$) in the battery material Li$_x$CoO$_2$ has been investigated by muon-spin relaxation ($\mu^+$SR). Based on the experiments in zero-field and weak longitudinal-fields at temperatures up to 400 K, we determined the fluctuation rate ($\nu$) of the fields on the muons due to their interaction with the nuclear moments. Combined with susceptibility data and
Magnetism of a misfit layered cobaltite (Ca2Co4/3Cu2/3O4)RSx (CoO2) (x ∼ 0.62, RS denotes a rocks... more Magnetism of a misfit layered cobaltite (Ca2Co4/3Cu2/3O4)RSx (CoO2) (x ∼ 0.62, RS denotes a rocksalt-type block) was investigated by a positive muon spin rotation and relaxation (µ+SR) experiment. A transition to an incommensurate (IC) spin density wave (SDW) state was found below 180 K (= T on C ); and a clear oscillation due to a static internal magnetic field was observed below 140 K (= TC). Furthermore, an anisotropic behavior of the zero-field µ+SR experiment indicated that the IC-SDW propagates in the a-b plane, with oscillating moments directed along the c axis. These results were quite similar to those for the related compound (Ca2CoO3)RS0.62(CoO2), i.e., Ca3Co4O9. Since the IC-SDW field in (Ca2Co4/3Cu2/3O4)RS0.62(CoO2) was approximately same to those in pure and doped (Ca2CoO3)RS0.62(CoO2), it was concluded that the IC- SDW exist in the (CoO2) planes.
The magnetic nature of a novel one-dimensional compound NaCr2O4 with zigzag CrO2 chains has been ... more The magnetic nature of a novel one-dimensional compound NaCr2O4 with zigzag CrO2 chains has been studied by muon spin rotation and relaxation (μ+SR) and neutron diffraction (ND). It is found that NaCr2O4 undergoes an antiferromagnetic transition at TN = 125 K, below which the Cr moments in each zigzag chain align ferromagnetically along the c-axis but antifer- romagnetically along the a-axis between adjacent zigzag chains. For the solid solution system Ca1−xNaxCr2O4, μ+SR measurements reveal the evolution of a complex magnetic order with increasing Ca content (1 − x), which finally enters into an incommensurate AF ordered state below TN = 21 for CaCr2O4.
In order to elucidate the dependence of the magnetic ground state on the Ca content (x) in Sr1−xC... more In order to elucidate the dependence of the magnetic ground state on the Ca content (x) in Sr1−xCaxCo2P2 (0 ≤ x ≤ 1, ThCr2Si2-type structure), we have performed muon spin rotation and relaxation (μ+SR) experiments on Sr1−xCaxCo2P2 powder samples mainly in a zero applied field. The end member compound, SrCo2P2, is found to be paramagnetic down to 19 mK. As x increases, such a paramagnetic ground state is observed down to 1.8 K until x = 0.45. Then, as x increases further, a short-range antiferromagnetic (AF) ordered phase appears at low temperatures for 0.48 ≤ x ≤ 0.75, and finally, a long-range AF ordered phase is stabilized for x > 0.75. The internal magnetic field of the other end member compound, CaCo2P2, is well consistent with that of the A-type AF order state, which was proposed from neutron scattering experiments. The phase diagram determined with μ+SR is different from that proposed by macroscopic measurements. For an isostructural compound, LaCo2P2, static magnetic order...
(http://www.tytlabs.com/review/issue/rcw.cgi?file=462_029sugiyama.pdf&PASS=1) In this paper, we w... more (http://www.tytlabs.com/review/issue/rcw.cgi?file=462_029sugiyama.pdf&PASS=1) In this paper, we will give an introduction to the method itself but also summary of our muon spin relaxation work on Li-diffusion in battery positive electrode materials. Furthermore, we will show that the method is not limited to studying only Li-diffusion but can also be extended to other physical and/or electrochemical properties in lithium transition-metal oxides.
In order to investigate the microscopic magnetic nature of a sodium phospho-olivine, we have meas... more In order to investigate the microscopic magnetic nature of a sodium phospho-olivine, we have measured μ+SR spectra for NaxFePO4 using a powder sample in the temperature range between 2 and 500 K. ZF-μ+SR measurements below 200 K at TRIUMF showed the appearance of static magnetic order below TN= 61 K, where the susceptibility-vs.-temperature curve exhibits a sharp maximum due to an antiferromagnetic (AF) transition. The wide distribution found for the internal magnetic field (Hint) was explained by the formation of AF order with the spread in Hint due to random distribution of Na vacancies. At higher temperatures, the ZF-spectrum for Na0.7FePO4, obtained at J-PARC, is found to change from a low-T static behavior to a high-T dynamic behavior above 300 K. This is consistent with the fact that Na+ ions are reversibly extracted from and intercalated into the NaxFePO4 lattice, while there is no NMR study on Na-diffusion in NaxFePO4 due to large Fe moments.
In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-$\... more In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-$\mu^+$SR spectra for the Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ powder samples with $x=0$, 0.2, 0.4, 0.5, 0.6, 0.8, and 1. Due to a characteristic time window and spatial resolution of $\mu^+$SR, the obtained phase diagram was found to be rather different from that determined by magnetization measurements. That is, as $x$ increases from 0, a Pauli-paramagnetic phase is observed even at the lowest $T$ measured (1.8~K) until $x=0.4$, then, a spin-glass like phase appears at $0.5\leq x\leq0.6$, and then, a phase with wide field distribution probably due to incommensurate AF order is detected for $x=0.8$, and finally, a commensurate $A$-type AF ordered phase (for $x=1$) is stabilized below $T_{\rm N}\sim80~$K. Such change is most likely reasonable and connected to the shrink of the $c$-axis length with $x$, which naturally enhances the magnetic interaction between the two adjacent Co planes.
Thanks to the unique power of muon-spin spectroscopy, we found that the quasi-one-dimensional Co-... more Thanks to the unique power of muon-spin spectroscopy, we found that the quasi-one-dimensional Co-Rh oxides An+2CoRhnO3n+3 (A = Ca, Sr; n=1, 2, and 3) exhibit a two-dimensional antiferromagnetic transition that ranges from TN^on=185 K for n=1 to 125 K for n=3 with a transition width (deltaT) of about 80 K. The variation of TN^on with n is explained by the increase in the distance between the neighboring CoRhnO3n+3 chains. Static magnetic order is observed below the endpoint of TN (=TN^on-deltaT) for each of the three samples. The existence of the two-frequency components in the ZF-spectrum indicates the appearance of ferrimagnetic order for Ca3CoRhO6 below 20 K.
Proceedings ICT'03. 22nd International Conference on Thermoelectrics (IEEE Cat. No.03TH8726), 2003
ABSTRACT Magnetism of misfit layered cobaltites, [Ca2CoO3]0.62RS[CoO2] and [Ca2Co43/Cu23/O4]0.62R... more ABSTRACT Magnetism of misfit layered cobaltites, [Ca2CoO3]0.62RS[CoO2] and [Ca2Co43/Cu23/O4]0.62RS[CoO2] (RS denotes a rocksalt-type block), was investigated by a positive muon spin rotation and relaxation (μ+SR) experiment. For the former cobaltite, a transition to an incommensurate (IC) spin density wave (SDW) state was found below 100 K (=TSDWon) and a clear oscillation due to a static internal magnetic field was observed below 30 K (=TSDW). For the latter cobaltite, TSDWon=180 K and TSDW=140 K, respectively. The wide transition width (= 40-70 K) suggested that a short-range IC-SDW order appeared below TSDWon and a long-range order completed below TSDW. Furthermore, an anisotropic behavior of the zero-field μ+SR spectra on the c axis aligned samples indicated that the IC-SDW propagates in the a-b plane, with oscillating moments directed along the c axis. These results suggest that the IC-SDW exist not in the rocksalt-type block but in the CoO2 plane.
Proceedings ICT'03. 22nd International Conference on Thermoelectrics (IEEE Cat. No.03TH8726), 2003
ABSTRACT In order to apply layered cobaltites to thermoelectric (TE) devices, we need aligned cer... more ABSTRACT In order to apply layered cobaltites to thermoelectric (TE) devices, we need aligned ceramics to exploit their superior in-plane TE properties. Here, we report the preparation and characterization of c-axis aligned [Ca2CoO3]0.62[CoO2] (CCO) ceramics by the reactive templated grain growth (RTGG) method. As reactive templates, we synthesized platelike β-Co(OH)2 particles by a precipitation method. The template particles were mixed with a complementary reactant, CaCO3, and aligned by a tape-casting. Upon heat treatment, they reacted to form a CCO ceramic with almost perfectly c-alignment (Lotgering's orientation degree, f > 0.99). The highly textured ceramic shows significantly large in-plane electrical conductivity (σab): i.e., the value of σab was 2.61 × 104 S/m at 1060 K, where the value is around 60 % of that of a single crystal. We conclude that the RTGG method must be an effective and versatile technique for the preparation of large-sized TE materials with high TE performances.
In order to clarify the reason why the hydrogen desorption temperature (Td) of MgH2 is lowered by... more In order to clarify the reason why the hydrogen desorption temperature (Td) of MgH2 is lowered by milling, we have studied the change in a local nuclear magnetic field with temperature by means of μ+SR. We have found a very clear oscillation in the ZF-spectrum at 2 K for the "milled" and "milled with Nb2O5" samples, while such oscillation is weaker for the "as-prepared" MgH2. It was also found that the oscillation signal is stable up to 250 K and is assigned mainly due to the formation of a Hμ+H system. At temperatures above ambient T, we also found that the ZF-μ+SR spectrum exhibits a static Kubo-Toyabe behavior due to the nuclear magnetic field of 1H. Furthermore, it was clarified that rapid H diffusion starts well below Td only in the milled samples, leading to the conclusion that the consequent enhanced diffusion rate in MgH2 is essential to accelerate the desorption reaction and to decrease Td.
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Papers by Jun Sugiyama