The effect of the annealing temperature on the local distortion of La0.67_{0.67}Ca0.33_{0.33}MnO3_3 thin films

Mn $K$-edge fluorescence data are presented for thin film samples (3000~\AA) of Colossal Magnetoresistive (CMR) La$_{0.67}$Ca$_{0.33}$MnO$_3$: as-deposited, and post-annealed at 1000 K and 1200 K. The local distortion is analyzed in terms of three contributions: static, phonon, and an extra, temperature-dependent, polaron term. The polaron distortion is very small for the as-deposited sample and increases with the annealing temperature. In contrast, the static distortion in the samples decreases with the annealing temperature. Although the local structure of the as-deposited sample shows very little temperature dependence, the change in resistivity with temperature is the largest of these three thin film samples. The as-deposited sample also has the highest magnetoresistance (MR), which indicates some other mechanism may also contribute to the transport properties of CMR samples. We also discuss the relationship between local distortion and the magnetization of the sample.Comment: 11 pages of Preprint format, 8 figures in one tar fil

Raman phonons as a probe of disorder, fluctuations and local structure in doped and undoped orthorhombic and rhombohedral manganites

We present a rationalization of the Raman spectra of orthorhombic and rhombohedral, stoichiometric and doped, manganese perovskites. In particular we study RMnO3 (R= La, Pr, Nd, Tb, Ho, Er, Y and Ca) and the different phases of Ca or Sr doped RMnO3 compounds as well as cation deficient RMnO3. The spectra of manganites can be understood as combinations of two kinds of spectra corresponding to two structural configurations of MnO6 octahedra and independently of the average structure obtained by diffraction techniques. The main peaks of compounds with regular MnO6 octahedra, as CaMnO3, highly Ca doped LaMnO3 or the metallic phases of Ca or Sr doped LaMnO3, are bending and tilt MnO6 octahedra modes which correlate to R-O(1) bonds and Mn-O-Mn angles respectively. In low and optimally doped manganites, the intensity and width of the broad bands are related to the amplitude of the dynamic fluctuations produced by polaron hopping in the paramagnetic insulating regime. The activation energy, which is proportional to the polaron binding energy, is the measure of this amplitude. This study permits to detect and confirm the coexistence, in several compounds, of a paramagnetic matrix with lattice polaron together with regions without dynamic or static octahedron distortions, identical to the ferromagnetic metallic phase. We show that Raman spectroscopy is an excellent tool to obtain information on the local structure of the different micro or macro-phases present simultaneously in many manganites.Comment: Submitted to PR

Phase diagram of the La1−x_{1-x}Cax_{x}MnO3_{3} compound for 0.5≤x≤0.90.5\leq x\leq 0.9

We have studied the phase diagram of La$_{1-x}$Ca$_{x}$MnO$_{3}$ for $0.5\leq x\leq 0.9$ using neutron powder diffraction and magnetization measurements. At 300 K all samples are paramagnetic and single phase with crystallographic symmetry $Pnma$. As the temperature is reduced a structural transition is observed which is to a charge-ordered state only for certain x. On further cooling the material passes to an antiferromagnetic ground state with Neel temperature $T_N$ that depends on x. For $0.8\leq x\leq 0.9$ the structural transformation occurs at the same temperature as the magnetic transition. Overall, the neutron diffraction patterns were explained by considering four phase boundaries for which La$_{1-x}$Ca$_x$MnO$_3$ forms a distinct phase: the CE phase at $x=0.5-0.55$, the charge-ordered phase at x=2/3, the monoclinic and C-type magnetic structure at $x=0.80-0.85$ and the G-type magnetic structure at x=1. Between these phase boundaries the magnetic reflections suggest the existence of mixed compounds containing both phases of the adjacent phase boundaries in a ratio determined by the lever rule

Ag 6Mo 2O 7F 3Cl: A new silver cathode material for enhanced ICD primary lithium batteries

As a potential cathode material for the ICD lithium battery, one advantage of Ag 6Mo 2O 7F 3Cl (SMOFC) Is its enhanced gravimetric capacity of ca. 133 mAh/g above 3 V (vs Li +/Li) delivered by two biphasic transitions at 3.46 and 3.39 V (vs Li +/Li). The unique crystal structure of SMOFC enables a high sliver ion conduction: σ ⊥[001] = 3.10 -2 S/cm (±2.10 -2 S/cm) and σ// [001] = 4.10 -3 S/cm (±2.10 -3 S/cm) and, hence, an excellent discharge rate capability. Lithium insertion has been monitored by in situ XRD measurements with HRTEM investigations. There is a linear isotropic collapse of the structure leading to a fully amorphous structure beyond four Inserted lithiums. © 2010 American Chemical Society

Room-Temperature synthesis leading to nanocrystalline Ag2V 4O11

This work highlights a roomerature composition study of the Ag 2O/V2O5/HF(aq) ternary system, leading to the precipitation of either various silver vanadates having Ag/V ratios from 1/2 to 3/1 or the new silver vanadium oxyfluoride compounds Ag 4V2O6F2 and Ag3VO 2F4, and a synthetic procedure that affords nanocrystalline Ag2V4O11 (SVO) at room temperature. The as-precipitated SVO particles exhibit an acicular morphology, 10-15 - 50-200 nm in size, and present a peculiar reactivity vs lithium notably through a Ag+/Li+ displacement reaction that progresses in a reversible fashion. This step forward thus enables the reversible and simultaneous combination of two active redox processes (silver and vanadium), providing a significant enhancement in the cathode gravimetric capacity of 320 mAh/g at C rate and more than 250 mAh/g at 5C. © 2010 American Chemical Society

Room temperature synthesis of the larger power, high silver density cathode material Ag 4V 2O 6F 2 for implantable cardioverter defibrillators

New cathode materials will lead to technological advances for implantable cardioverter defibrillators, ICDs, such as reduced size and increased performance of the device. While the industry standard silver vanadium oxide Ag 2V 4On 11 exhibits great chemical/ electrochemical stability, dense silver oxide fluoride materials are advantageous because of high crystal density that can result in an increased capacity above 3 V. This report highlights the reactivity at room temperature between Ag 2O and V 2O 5 in an aqueous HF solution which affords a rapid precipitation of sub-micrometer sized Ag 4V 2O 6F 2 (SVOF), a high capacity Li-battery cathode material. This system opens new and novel synthetic strategies in the design of new oxide fluoride materials. © 2009 American Chemical Society

Structural, Electrical, and Optical Properties of the Tetragonal, Fluorite-Related Zn<inf>0.456</inf>In<inf>1.084</inf>Ge<inf>0.460</inf>O<inf>3</inf>

International audienceWe report the discovery of Zn0.456In1.084Ge0.460O3, a material closely related to bixbyite. In contrast, however, the oxygen atoms in this new phase occupy 4 Wyckoff positions, which result in 4 four-coordinate, 24 six-coordinate (2 different Wyckoff positions), and 4 eight-coordinate sites as compared to the 32 six-coordinate (also 2 different Wyckoff positions) sites of bixbyite. This highly ordered material is related to fluorite, Ag6GeSO8, and -UO3 and is n-type with a bulk carrier concentration of 4.772 × 1014 cm-3. The reduced form displays an average room temperature conductivity of 99(11) S·cm-1 and an average optical band gap of 2.88(1) eV. These properties are comparable to those of In2O3, which is the host material for the current leading transparent conducting oxides. The structure of Zn0.456In1.084Ge0.460O3 is solved from a combined refinement of synchrotron X-ray powder diffraction and time-of-flight neutron powder diffraction and confirmed with electron diffraction. The solution is a new, layered, tetragonal structure in the I41/amd space group with a = 7.033986(19) Å and c = 19.74961(8) Å. The complex cationic topological network adopted by Zn0.456In1.084Ge0.460O3 offers the potential for future studies to further understand carrier generation in -3 eV oxide semiconductors. © 2015 American Chemical Society

Structural, Electrical, and Optical Properties of the Tetragonal, Fluorite-Related Zn0.456In1.084Ge0.460O3

We report the discovery of Zn0.456In1.084Ge0.460O3, a material closely related to bixbyite. In contrast, however, the oxygen atoms in this new phase occupy 4 Wyckoff positions, which result in 4 four-coordinate, 24 six-coordinate (2 different Wyckoff positions), and 4 eight-coordinate sites as compared to the 32 six-coordinate (also 2 different Wyckoff positions) sites of bixbyite. This highly ordered material is related to fluorite, Ag6GeSO8, and -UO3 and is n-type with a bulk carrier concentration of 4.772 × 1014 cm-3. The reduced form displays an average room temperature conductivity of 99(11) S·cm-1 and an average optical band gap of 2.88(1) eV. These properties are comparable to those of In2O3, which is the host material for the current leading transparent conducting oxides. The structure of Zn0.456In1.084Ge0.460O3 is solved from a combined refinement of synchrotron X-ray powder diffraction and time-of-flight neutron powder diffraction and confirmed with electron diffraction. The solution is a new, layered, tetragonal structure in the I41/amd space group with a = 7.033986(19) Å and c = 19.74961(8) Å. The complex cationic topological network adopted by Zn0.456In1.084Ge0.460O3 offers the potential for future studies to further understand carrier generation in -3 eV oxide semiconductors. © 2015 American Chemical Society

Structural, Electrical, and Optical Properties of the Tetragonal, Fluorite-Related Zn<inf>0.456</inf>In<inf>1.084</inf>Ge<inf>0.460</inf>O<inf>3</inf>

We report the discovery of Zn0.456In1.084Ge0.460O3, a material closely related to bixbyite. In contrast, however, the oxygen atoms in this new phase occupy 4 Wyckoff positions, which result in 4 four-coordinate, 24 six-coordinate (2 different Wyckoff positions), and 4 eight-coordinate sites as compared to the 32 six-coordinate (also 2 different Wyckoff positions) sites of bixbyite. This highly ordered material is related to fluorite, Ag6GeSO8, and -UO3 and is n-type with a bulk carrier concentration of 4.772 × 1014 cm-3. The reduced form displays an average room temperature conductivity of 99(11) S·cm-1 and an average optical band gap of 2.88(1) eV. These properties are comparable to those of In2O3, which is the host material for the current leading transparent conducting oxides. The structure of Zn0.456In1.084Ge0.460O3 is solved from a combined refinement of synchrotron X-ray powder diffraction and time-of-flight neutron powder diffraction and confirmed with electron diffraction. The solution is a new, layered, tetragonal structure in the I41/amd space group with a = 7.033986(19) Å and c = 19.74961(8) Å. The complex cationic topological network adopted by Zn0.456In1.084Ge0.460O3 offers the potential for future studies to further understand carrier generation in -3 eV oxide semiconductors. © 2015 American Chemical Society