MnO6 Octahedron Research Articles

Structural-distortion modes and transport properties of La0.5Ca0.5MnO3 by co-doping Dy3+ and Sr2+ ions

La0.5-xDyxCa0.5-ySryMnO3 (x=0, 0.05, 0.08, 0.1, 0.14, 0.16, 0.2) polycrystalline samples were prepared by high-temperature solid-state reaction. The A-site disordering is increased with the doping concentration x, and meanwhile the average ionic radius of A-site is kept constant. X-ray diffraction and Raman spectroscopy were combined to investigate the microstructural distortion of MnO6 octahedron. Results show that the rotational vibration (RV) is the dominant distortion mode. With the A-site disordering increasing, RV mode is obviously hardened, and the Jahn-Teller distortion is enhanced. Properties investigation shows that the insulation is strengthened because of FM double exchange effect suppressed with A-site disordering increasing, and the magnetoresistance effect is weakened. A relatively significant magnetoresistance effect was observed in the low temperature region for the high-doped concentration sample, which may be related to the strong magnetic moment of Dy3+.

Large magnetocaloric effect in La0.75Ca0.25–xNaxMnO3 (0 ≤ x ≤ 0.10) manganites

We have studied the effect of a partial substitution of Ca2+ by Na+ on the structural, magnetic and magnetocaloric properties of the mixed valence perovskites $${\text{La}}_{{{0}{\text{.75}}}} {\text{Ca}}_{{{0}{\text{.25 - }}x}} {\text{Na}}_{x} {\text{MnO}}_{{3}}$$ (0 ≤ x ≤ 0.10), prepared by the flux method. X-ray diffraction studies revealed that our samples crystallize in the orthorhombic structure with a Pbnm space group. Rietveld analysis showed that MnO6 octahedron has a little distortion and that θMn–O–Mn bond angles increase with increasing Na+ content. The field cooled (FC) and zero field cooled (ZFC) magnetizations indicated that our samples have a paramagnetic-ferromagnetic phase transition, when decreasing temperature. A small deviation was observed between FC and ZFC curves. This deviation can be explained by the competition between the ferromagnetic and antiferromagnetic interactions, leading to a glassy behavior. The Curie temperature, TC, increased from 268 K for x = 0 to 278 K for x = 0.10. The magnetizations isotherms of our compounds, with a second-order phase transition, were investigated. For the x = 0.10 sample, the maximum of the magnetic entropy change was found to be 3.15 and 6.44 J kg−1 K−1, under an applied magnetic field of 2 and 5 T, respectively. Moreover, it has important relative cooling power values of about 134.82 and 317.79 J kg−1, under the same applied magnetic field. In addition, rescaled entropy data collapsed into the same curve, which indicates the universal behavior for the magnetocaloric effect (MCE) in our compounds. These materials could be potential candidates as working substances in magnetic refrigeration.

Structural evolution and multiferroic properties in the vicinity of MPB of Ca2Bi4Ti5-xMnxO18 solid solutions

The crystal structure transition and its effect on the multiferroic characteristics were investigated in Ca2Bi4Ti5-xMnxO18 (0 ≤ x ≤ 2) ceramics synthesized by the molten salt method. Mn substitution induces variations in a/b ratio and the distortion degree of oxygen octahedrons, which can effectively regulate the multiferroic properties at room temperature. The structure changes from orthorhombic B2cb to tetragonal I4/mmm with a morphotropic phase region forming in the ceramic at x = 1.5. The Raman spectra manifest that Mn substitution not only alters the vibration mode of MnO6 octahedron but also changes the structural environment of TiO6 in the perovskite lattice. The average grain size increases gradually and the grain size distribution gets homogeneous with the increase in Mn content. All the ceramics show a lossy dielectric behavior. The addition of Mn results in a significant enhancement in macroscopic magnetization and dielectric properties. In addition to this, the magnetoelectric coupling effect has also been improved and a maximum magnetoelectric coefficient of α ≈ 12.3 mV/(cm·Oe) is attained for the ceramic sample with x = 1.5.

Structural and magnetic properties of La1-x⎕xMnO3 (x = 0.1; 0.2 and 0.3) manganites

The intrinsic objective of this work is to investigate the structural (RX, MEB, TGA and IR) and magnetic properties of La1 La1-x⎕xMnO3 (x = 0.1; 0.2 and 0.3) series prepared through the sol–gel method. All these systems crystallize in the rhombohedral structure, $$ {{\rm R}\bar{3}{\rm c}} $$ space group, with the presence of a secondary phase for x = 0.3. We recorded the increase of a unit cell volume when the La deficiency amount increases, which refers to the fact that the vacancy is characterized by a radius other than zero. Another point that can be quoted is the increase of Mn–O–Mn bond angle and the decrease of Mn–O length with lanthanum deficiency (x), confirming the increase of the unit cell volume. The evaporation of water rose by the weight loss as a function of temperature in all samples. The FT-IR measurement revealed one peak corresponding to the Mn–O bond; this can be explained by the Jahn–Teller effect where the Mn ion makes an internal movement against the MnO6 octahedron. The thermal variation of the magnetization indicates the existence of a paramagnetic–ferromagnetic transition at Curie temperature with the increase of lanthanum deficiency. Saturation magnetization and Curie temperature increased with x (0.1; 0.2 and 0.3) deficiency. Hysteresis cycles confirm the ferromagnetic character at low temperatures and paramagnetic state with temperature increase. The increase of saturation magnetization can be accounted for in terms of the change of high spin Mn3+ to low spin Mn4+. Departing from the study of magnetic properties in terms of Arrott plots, the nature of magnetic transitions proves to be of second order.

La0·7Ca0.3−xSrxMnO3:Ag0.2 (0.0165 ≤ x ≤ 0.1) ceramics with large and stable TCR in different magnetic field environments

La0·7Ca0.3−xSrxMnO3:Ag0.2 (LCSMO:Ag) ceramics with varying strontium (Sr) content (x = 0.0165, 0.03, 0.05, 0.07, and 0.1) were synthesized using a combination of sol–gel and solid-state doping methods and studied as colossal magnetoresistance materials. Significant improvements in the peak temperature coefficient of resistivity (TCR) and resistivity (ρ) were observed across all ceramic samples when the mol% of Sr was adjusted. The low ρ and large TCR values resulted from a combination of two factors. First, the presence of Sr led to the increase in the grain size and decrease in the number of boundaries, which improved the electrical transport and reduced the boundary scattering effects. This resulted in additional improvement in the grain arrangement order. Second, the cell volume (Vcell) and octahedron volume (Voct) both decreased first and then increased. The MnO6 octahedron underwent gradual deformation into a flattened shape, which facilitated carrier migration and increased electrical sensitivity of the material. The ceramic with x = 0.03 maintained high and stable TCR values in different working environments, both without a magnetic field (TCRo, 54.76% K−1) and in the presence of a vertical field (TCR⊥, 33.33% K−1). Furthermore, the material exhibited a low resistivity and a higher insulator–metal transition temperature (Tp). Performance differences among the samples were comprehensively and systematically explained by conducting cross magnetic field tests with field directions parallel and perpendicular to the flat surface of the bulk material, respectively. Overall, the findings of this study indicate that these ceramics act as promising candidates for future applications in information storage devices and magnetic sensors.

Surface modification by fluorine doping to increase discharge capacity of Li1.2Ni0.2Mn0.6O2 cathode materials

Anion doping is considered as an effective method to tap the potential of Li-rich materials to obtain more discharge capacity. Here, we prepare fluorine-doped Li1.2Ni0.2Mn0.6O2 materials by a low-temperature secondary sintering. Rietveld refinements of XRD show an increase in lattice parameters and indicate a wider Li+ diffusion channel after fluorine doping. From TEM and HRTEM images, it is observed that the fluorine-doped sample displays a more pronounced layered appearance, and partial lattice fringes are slightly curved which may be caused by the substitution of F for O to break the symmetry of MnO6 octahedron. The fitting results of XPS show that Mn is partially oxidized and the local electronic environment of O changes. The best one shows a discharge capacity of 288 mAh/g at 0.1 C with a Coulombic efficiency of 95.9% in the first lap. And it performs a capacity retention of 91.0% after 100 cycles at 0.2 C.

Dynamic exchange effect induced multi-state magnetic phase diagram in manganese oxide Pr1-xCaxMnO3

The crystal structure and magnetic properties of Pr1-xCaxMnO3 (PCMO) were investigated systematically. It is shown that the symmetry of the structure is improved with the increase of Ca2+ ions. At the same time, the distortion of the MnO6 octahedron is reduced due to the weakening of the Jahn-Teller (J-T) effect in the system. Magnetic characterization shows that the original ferromagnetic (FM) at the low doping range (x = 0.2, 0.3) begins to appear antiferromagnetic (AFM) at the half doping range (x = 0.4, 0.5). Such magnetic transition is derived from the dynamic competition between the double exchange (DE) effect and the super exchange (SE) effect. These two exchange effects are significantly affected by structural distortions and charge-ordered (CO) phases. The coexistence and transition of multiple magnetic states embody complex internal competition in PCMO. Analysis of its intrinsic mechanism is helpful for designing spintronic devices.

Dependence of the electrical and magnetic properties of La0.845Sr0.155MnO3:Ag0.4 ceramics on its sintering time

In this work, polycrystalline La0.845Sr0.155MnO3:Ag0.4 (LSMO:Ag) ceramics were synthesized via a combined sol–gel and solid-state method with various sintering times. The structure and unique electrical and magnetic properties of the synthesized ceramics were examined in detail. The optimized sintering temperature was determined to be 1723 K. At this temperature, by changing the sintering time from 5 to 14 h, the temperature coefficient of resistivity (TCR) and the magnetic resistance (MR) of the LSMO:Ag samples could be quickly improved. The results show that La3+ and Sr2+ ions were gradually substituted by Ag+ ions with increasing sintering time. The substitution resulted in changes to the Mn3+–O–Mn4+ pairs and a distortion of the MnO6 octahedron, which could be attributed to the double exchange (DE) and Jahn–Teller (JT) effects. At a sintering time of t = 10 h, a peak TCR value of 17.82% K−1 was attained and was achieved at room-temperature (Tk, 299.9 K). This work demonstrates an effective approach to obtain high TCR and MR values at room-temperature for uncooled manganite devices by optimizing the sintering time.

Evolutions of geometry and electronic state introduced by oxygen vacancy for CaMnO3 compound

Abstract The cell structures, locally micro-structures, combinations, electronic states as well as carrier transports induced by Oxygen vacancy for the CaMnO3 compound have been systematically investigated by pseudo-potential plane wave functions within the framework of density functional theory calculational method. The results reveal that the Oxygen vacant CaMnO2.75 has larger formation enthalpy than that of the intrinsic CaMnO3 and the Oxygen vacancy formation energy of CaMnO3 is as large as 7.10 eV. The Oxygen vacant CaMnO2.75 is harder to form than the intrinsic CaMnO3. The cubical orthorhombic structure tends to be rhombohedral. The lattice parameters a, b and c decrease simultaneously. The α and γ shrinks, the β increases. The lattice shrinkage induced by oxygen vacancy is anisotropic. The MnO6 octahedrons is twisted and it is shrinked along c and expanded along a. The bond strengths of Mn-O are all enhanced. There are six energy bands and the band gap is narrowed, the Fermi level is heightened and the electrons tend to occupy high energy bands. At the same time, the work function of electrons is lowered from 4.69872 eV to 4.00048 eV. The conductivity should be enhanced for Oxygen vacant CaMnO2.75, the O p and Mn d state electrons contribute most to the upper valance bands as well as the lower conduction bands, they jointly realize the conduction process.

Li and Mn-rich Li4Mn5O12–Li2MnO3 composite cathode for next generation lithium-ion batteries

Abstract Recently, the integration of spinel and layered structure received significant attentions to improve the electrochemical performance of the Lithium and manganese rich oxide material. In this work, Lithium-rich, Li4Mn5O12–Li2MnO3 composite is synthesized by the Sol-gel method. The structural and electrochemical performances of the composite materials are analyzed. X-ray diffraction result confirms the formation of spinel Li4Mn5O12 and layered Li2MnO3 mixed phase. Scanning electron microscopy image depicts the presence of an elongated particle with an average size of 50–60 nm. Transmission electron microscopy result clearly shows the existence of spinel and layered phase. Raman measurement result indicates the presence A1g, E2g and F2g vibration modes of MnO6 octahedron. Li4Mn5O12–Li2MnO3 composite cathode delivers a first discharge capacity of 318 mA h g−1 at 0.1C rate and retains the discharge capacity of 209 mA h g-1 at the 50th cycle. The capacity retention of the composite cathode is 89% after 50 charge-discharge cycles. Formation of a hybrid composite structure enhances the capacity, rate capability and structural stability of the Li4Mn5O12–Li2MnO3 cathode material.

Preparation and magnetic properties of o-LiMnO2

Pure o-LiMnO2 prepared by solid state reaction under Ar flow at 850 °C crystallizes in an orthorhombic symmetry (SG: Pmnm). Mn3+ with four unpaired electrons is subjected to a strong Jahn-Teller (J-T) distortion, where the MnO6 octahedron is significantly elongated (1.17%) along the c axis. In air, the oxide converts to spinel LiMn2O4 at ∼320 °C. The magnetic susceptibility of LiMnO2, measured between 4.2 and 900 K, indicates a long range order. The negative θP value (−790 K) reveals strong antiferromagnetic interactions between half-filled dz21 orbital. The predominant interaction is negative and occurs between Mn3+ and its next-nearest neighbors via O2− ions by super exchange with Mn3+-O: 2p-Mn3+ angle of 178°. Above 300 K, the susceptibility follows a Curie Weiss law with a magnetic moment of 5.26 μB consistent with the high spin state Mn3+ (t2g3 eg1) but slightly larger than the spin only contribution for the ground state 5Do. The susceptibility is field dependent down to 4.2 K and a spin canting has been detected at low temperature. As magnetic chains are separated by non-magnetic Li ones, the interactions are confined along the [1 1 0] direction and one can expect a good realization of one dimensional model. Therefore, the magnetic data have been fitted on the base of the isotropic model for finite linear chain in terms of intra-chain antiferromagnetic interactions using the Fisher model. The best fitting is obtained for a value of J/k = −60 K. The results are compared with those of the crednerite CuMnO2 with smaller J/k value (−33 K).

Preparation, Crystal Chemistry, and Hidden Magnetic Order in the Family of Trigonal Layered Tellurates A2Mn(4+)TeO6 (A = Li, Na, Ag, or Tl).

We report the first four magnetic representatives of the trigonal layered A2M(4+)TeO6 (here, M = Mn) family. Na2MnTeO6 was synthesized from NaMnO2, NaNO3, and TeO2 at 650-720 °C, but analogues for which A = Li and K could not be obtained by direct synthesis. However, those for which A = Li, Ag, and Tl (but not K) were prepared by exchange reactions between Na2MnTeO6 and the corresponding molten nitrates. The oxygen content was verified by redox titration. According to the X-ray diffraction Rietveld analysis, the four new compounds are isostructural with Na2GeTeO6, trigonal ( P3̅1 c), based on ilmenite-like layers of edge-shared oxygen octahedra occupied by Mn(4+) and Te(6+) in an ordered manner. These layers are separated by cations A, also in a distorted octahedral coordination. However, off-center displacement of Tl+ is so strong, due to the lone-pair effect, that its coordination is better described as trigonal pyramid. Each MnO6 octahedron shares two opposite faces with AO6 octahedra, whereas TeO6 octahedra avoid sharing faces. Besides this double-layered structure, Na2MnTeO6 was often accompanied by a transient triple-layered rhombohedral polytype. However, it could not be prepared as a single phase and disappeared on annealing at 700-720 °C. All A2MnTeO6 samples (A = Ag, Li, Na, or Tl) revealed the unusual phenomenon of hidden magnetic order. Low-field magnetic susceptibility data exhibit a Curie-Weiss type behavior for all samples under study and do not show any sign of the establishment of long-range magnetic order down to 2 K. In contrast, both the magnetic susceptibility in sufficiently high external magnetic fields and the zero-field specific heat unambiguously revealed an onset of antiferromagnetic order at low temperatures. The frustration index f = Θ/ TN takes values larger than the classical values for three-dimensional antiferromagnets and implies moderate frustration on the triangular lattice.

Structural stability and superior electrochemical performance of Sc-doped LiMn2O4 spinel as cathode for lithium ion batteries

Scandium doped LiScxMn2-xO4 compounds are synthesized by solid-state method, which show single phase with rod-like polyhedron morphology. The Sc-doping decreases the lattice parameter ‘a’ marginally due to the change in the inter-atomic distance of the metal oxide bonds as confirm by Rietveld refinement. In addition, the expansion of LiO4 tetrahedron and contraction of MnO6 octahedron by ∼0.01 Å upon doping are observed. The Sc2p3/2 peak at 402.5 eV and Sc2p1/2 peak at 407.2 eV in the XPS spectrum of LiSc0.06Mn1.94O4 confirms the presence of Sc in the spinel structure. The symmetric stretching of MnO bond of LiSc0.06Mn1.94O4 shifts lower value (∼4 cm−1) than that of LiMn2O4 indicating the occupancy of Sc3+ ion in the octahedral site. The diffusion coefficient value of LiSc0.06Mn1.94O4 (1 × 10−12cm2s−1) is one-order higher than that of undoped LiMn2O4 (1 × 10−13 cm2s−1). LiMn2O4 delivers a discharge capacity of 117 mAhg−1 at 1C with a capacity retention of 74% after 500 cycles, whereas under similar condition LiSc0.06Mn1.94O4 delivers a discharge capacity of 114 mAhg−1 with a capacity retention of >90%. LiSc0.06Mn1.94O4 also delivers excellent rate capability due to high diffusion coefficient and less charge transfer resistance compared to the parent compound. The structure and morphology of the Sc-doped electrode after 500 cycles remains intact without any formation of Mn-rich agglomeration suggest that the reduction of Mn2+ ion dissolution as well as Jahn-Teller distortion. Hence LiSc0.06Mn1.94O4 can be a potential cathode material for lithium ion batteries.

Intrinsic exchange bias effect in strain-engineered single antiferromagnetic LaMnO3 films

In this work, epitaxial growth of LaMnO3 thin films on different substrates using pulsed laser deposition under tensile and compressive strain was studied. The intrinsic exchange bias effect was observed in the single A-type antiferromagnetic LaMnO3 films no matter whether the tensile or compressive strain was supplied by the substrates. Due to the lattice mismatch between the film and different substrates, the intense strain can induce MnO6 octahedral rotation in the bottom region of the film neighboring the substrate, which leads to the distortion of MnO6 octahedron and the net magnetic behavior. However, the upper part maintains the original A-type antiferromagnetic order due to strain relaxation. The exchange bias effect in single films is attributed to the coupling between the bottom canted magnetic part and the upper antiferromagnetic region. The observation of exchange bias in single films on different substrates enables the emergence of a new class of biasing components in spintronics, which are based on strain-engineering.

Influence of Mn doping on microstructure, optical, dielectric and magnetic properties of BiFeO3 nanoceramics synthesized via sol–gel method

The present work embodies studies on the structure, optical, electrical and magnetic properties of BiFe1-xMnxO3 (0 ≤ x ≤ 0.06) nanoceramics synthesized through sol-gel process. The prepared compositions were examined through several analytical techniques. Rietveld refinement analysis of the x-ray diffraction (XRD) data confirms rhombohedral crystal structure with R3c space group for all the samples and the crystallite size varies in the range of 14–17 nm. Electron microscopy (SEM/TEM)) images exhibit non-uniform surface morphology and agglomerated nature of the nanoparticles. The elemental compositions were established from energy dispersive x-ray (EDX) analysis. The bending/stretching vibration modes in the samples have been identified through Fourier transform infrared (FTIR) spectroscopy. A slight variation in the optical band gap is observed with the Mn doping. Frequency dependent dielectric measurements at room temperature reveal maximum value of the dielectric constant for 4% Mn doped BiFeO3 at lower frequencies. The magnetic hysteresis (M-H) loops at room temperature show ferromagnetic nature of all the prepared samples associated with the Jahn Teller distortion of MnO6 octahedron. A suppression in the saturation magnetization is observed for the higher Mn concentration samples. Thus, the appropriate doping of Mn ions can improve the dielectric and magnetic properties of the BiFeO3 system.

Half metallic ferromagnetism in PrMnO3 orthorhombic stable phase: an experimental and theoretical investigation

This work investigates the properties of PrMnO3 and transition metal Zr doped perovskite manganites under the framework of theoretical and experimental prospective. The theoretical study involves the investigation of structural properties as well as electronic properties using density functional theory with PBE-sol approximation and the mBJ method using WIEN2K code. While in the experimental part, we calculated the structural, surface morphology and dielectric properties of Pr1−xZrxMnO3 for x = 0 and x = 0.25 using x-ray Diffractometer, Field Emission Scanning electron microscopy (FESEM), FTIR and LCR Meter, whereas samples were synthesized by sol-gel auto-combustion method. The XRD pattern reveals that the structure of PrMnO3 compound crystallized in perovskite orthorhombic phase with the space group Pbnm. Crystallite size of PrMnO3 decreases by the addition of 25% Zr and unit cell volume is found to be increased by the substitution of 25% Zr. The FTIR spectra displayed the Mn-O-Mn bonds which are related to the MnO6 octahedron and confirms the ABO3 perovskite characteristic vibration. SEM results show that with the addition of 25% Zr microstructures of prepared nanoparticles exhibit a bit agglomeration of very fine particles with smooth and round edges. EDX plot confirms the existence of the elements. LCR meter data reveals that by the substitution of Zr in PrMnO3 dielectric constant and dielectric loss factor of samples increases. Impedance analyses disclosed that the total impedance of the material decreases with the doping of Zr. The theoretically calculated structural properties; density of states, band structures and magnetic order reveals the half metallic nature of PrMnO3 in orthorhombic stable phase.

Effect of co-doping of Fe and Gd on the structural, morphological and dielectric properties of LaMnO3 nanocrystallites using Sol-Gel technique

In order to study the structural, surface morphological and dielectric properties of La1−xFexMn1−yGdyO3 for x = 0, 0.25 and y = 0, 0.04, 0.06, 0.08, nanocrystallites have been synthesized by sol-gel auto combustion method. The x-ray diffraction (XRD) patterns reveal that the structure of crystallite size increases by increasing the Gd concentration. The unit cell volume decreases by the substitution of 25% Fe, while the unit cell volume increases by the substitution of Gd upto 8%. The Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectra show the formation of Mn–O–Mn bonds which are related to the MnO6 octahedron and confirm the existence of ABO3 perovskite characteristic vibration. Field emission scanning electron microscope (FESEM) results show that Fe and Gd influence the surface morphology of the samples and the samples with 8% Gd concentration causes the agglomeration of particles. Energy Dispersive x-ray (EDX) Spectroscopy plot shows the presence of all the elements and EDX plot of all the samples strongly match with a standard values of La, Fe, Mn, Cl and oxygen (O). LCR meter data tells that by increasing concentration of Gd in LaMnO3, dielectric constant and dielectric loss factor of samples increase. Impedance analysis reveals that total impedance of the material decreases with the increase of Gd doping. Complex impedance analysis has been explored by the cole-cole plot to examine the involvement of grain, grain boundary, and interfacial effects individually. Cole-cole plot indicates that Gd doping reduces the grain boundaries and forms a large semicircle.

Effects of A-site cation disordering on the transport properties of half-doping La0.5Ca0.5MnO3 manganites

Polycrystalline samples of La0.5−xYxCa0.5−ySryMnO3 (0 ≤ x ≤ 0.20, 0 ≤ y ≤ 0.22) were synthesized by solid state reaction method. The degree of A-site disorder increases linearly with increasing doping content. Structural analysis of X-ray diffraction shows that samples crystallize in a pure orthorhombic Pnma phase and antisymmetry stretching appears in MnO6 octahedron. Raman spectra illustrate rotationlike mode and antisymmetry stretching mode are both hardened with increasing A-site disordering, indicating the Jahn-Teller distortion strengthened. The metal-insulator transition temperature and MR values are found to decrease with increasing A-site disordering. The suppression of metallic behavior is ascribed to the enhancement of Jahn-Teller effect caused by increasing A-site disordering.

The Structure of Mn(acac)3 -Experimental Evidence of a Static Jahn-Teller Effect in the Gas Phase.

The structure of free manganese(III) tris(acetylacetonate) [Mn(acac)3 ] was determined by mass-spectrometrically controlled gas-phase electron diffraction. The vapor of Mn(acac)3 at 125(5) °C is composed of a single conformer of Mn(acac)3 in C2 symmetry with the central structural motif of a tetragonal elongated MnO6 octahedron and 47(2) mol % of acetylacetone (Hacac) formed by partial thermal decomposition of Mn(acac)3 . Three types of Mn-O separations have been refined (rh1 =2.157(16), 1.946(5), and 1.932(5) Å. We have found no indication for a significant deviation of the -C-C-C-O-Mn-O- six-membered rings from planarity, which is observed in the solid state.

Modulation of Jahn-Teller effect on magnetization and spontaneous electric polarization of CuFeO2

CuFe0.99Mn0.01O2 and CuFe0.99Co0.01O2 single crystal samples are grown by a floating zone technique and their magnetization and spontaneous electric polarization have been investigated. Similarly with pure CuFeO2, an obviously anisotropic magnetization and spontaneous electric polarization were observed in the both doped samples, and their phase transition critical fields and temperatures are directly doping ion dependent. Considering the different d-shell configuration and ionic size between Mn3+, Co3+ and Fe3+ ions, in which the Mn3+ ion with Jahn-Teller (J-T) effect has different distortion on the geometry frustration from both of Fe3+ and Co3+ ion. Since for Mn3+ ion, the orbital splitting results from the low-symmetry J-T distortion in a crystal-field environment leads to a distorted MnO6 octahedron, which different from undistorted FeO6 and CoO6 octahedrons. The strain between distorted and undistorted octahedrons produces different effects on the spin reorientation transition and spontaneous electric polarization. Although the pure CuFeO2 has a very strong and robust frustration, the presence of the strain due to the random distribution of distorted MnO6 octahedron and undistorted CoO6 (FeO6) octahedrons leads to its spin reorientation transitions and spontaneous electric polarization different from CuFeO2.