Site Ionic Radius Research Articles

Comprehensive analysis on the effect of ionic size and size disorder parameter in high entropy stabilized ferromagnetic manganite perovskite

A series of high entropy manganites, $(5{A}_{0.2}){\mathrm{MnO}}_{3}$, were prepared with varying the average ionic radius, $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$, and cationic size disorder, ${\ensuremath{\sigma}}^{2}$, on the $A$ site. All the samples were synthesized using the citrate sol-gel method. In all the compounds, the manganese valence was kept unaltered with reference to the conventional manganite ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_{3}$, which is ferromagnetic with ${T}_{C}\ensuremath{\sim}365$ K. The ratio of manganese valance is found to be unaltered as confirmed using x-ray photoelectron studies. The samples were characterized by powder x-ray diffraction, field-emission scanning electron microscopy (FE-SEM), energy dispersive x-ray analysis, elemental mapping, and magnetization measurements. These high entropy oxides show the variation in Curie temperature over a wide range from 85 to 273 K depending on the average $A$-site ionic radius, $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$. A drastic drop down in the ferromagnetic transition temperature of ${T}_{C}=365$ K for ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_{3}$ with $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}=1.2536\phantom{\rule{0.16em}{0ex}}\AA{}$ to ${T}_{C}=137\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for (${\mathrm{La}}_{0.2}{\mathrm{Nd}}_{0.2}{\mathrm{Gd}}_{0.2}{\mathrm{Sr}}_{0.2}{\mathrm{Ba}}_{0.2}$)${\mathrm{MnO}}_{3}$ of comparable $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}=1.2532\phantom{\rule{0.16em}{0ex}}\AA{}$ can be attributed to the high entropy and/or cationic size disorder effect. The variation of ${T}_{C}$ with $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$ for the whole series of high entropy manganites does not follow the expected linear behavior; rather, it follows opposite traces of the variation in ${\ensuremath{\sigma}}^{2}$ with $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$. However, ${T}_{C}$ shows almost linear behavior with ${\ensuremath{\sigma}}^{2}$ except for the sample with lowest $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$. This result suggests that the local cationic disordering is more important than the average cationic size in ferromagnetic high entropy manganites. Unlike the conventional system in these high entropy oxides, the ferromagnetic state is not suppressed; only the length scale of the double exchange mediated long-range ferromagnetic interaction is transformed to localized ferromagnetic clusters without losing the ferromagnetic identity. The presence of multiple $A$-site cations in high entropy oxides results in a local deformation of the ${\mathrm{MnO}}_{6}$ octahedra. This possibly increases the carrier localization followed by reducing the length scale of the double exchange interaction.

Predicting Experimental Formability of Hybrid Organic-Inorganic Perovskites via Imbalanced Learning.

Hybrid organic-inorganic perovskites (HOIPs) have gained lots of attention in the photovoltaic field, but their further development is restrained by contaminant and stability. More potential HOIPs should be explored for photovoltaic devices. In this work, we collected 539 HOIPs and 24 non-HOIPs experimentally synthesized to explore novel compositions of HOIPs. An imbalanced learning was carried out, and the best classification model achieved a leaving-one-out cross-validation accuracy of 100.0% and a test accuracy of 96.1%. The A site atomic radii (ARA), A site ionic radius (IRA), and tolerance factor (tf) were identified as the most important features. ARA < 2.72 Å, IRA < 2.65 Å, and tf < 1.01 contributed to perovskite formability, and the formability possibilities of the corresponding samples were over 90.0%. Potential A site organic fragments were identified for perovskite solar cells, such as dimethylamine, hydroxylamine, hydrazine, etc. Finally, three new Sn-Ge mixed systems of HOIPs were successfully synthesized, which was consistent with the model predictions.

A2B2O7 (A= La, Pr, Nd, Sm, Gd and B Ti, Zr, Sn) ceramics for mild-temperature NO2 sensing and reduction

Abstract The present work demonstrates the design and synthesis of A2B2O7 (A = La, Pr, Nd, Sm, Gd and B = Ti, Zr, Sn) ceramics to fabricate NO2 sensors for efficient NO2 sensing and reduction at mild temperature. To clarify the sensing mechanism of NO2 sensor, the electron layer mechanism of rare-earth cations at A site and different ionic radius of B-site cations are investigated to discuss the difference from the NO2 sensing and reduction. The unique electronic structure of Pr3+([Xe]4f2) endows the different band structure and the variable valence in nature with +3 and + 4 oxidation states, which would induce different electronic transport, resulting in enhanced NO2 sensing performances and reduction reaction. According to A2B2O7 structure, the activation energy of oxygen hopping is clarified through comparing different ionic radius of B cations, and the surface oxygen species providing a transfer station for oxygen hopping of solid electrolyte are analyzed by various characterization techniques. The results show that high sensitivity obtained over pure Pr2Sn2O7 without any doping at A or B site is as high as 124 nA/ppm towards 25–100 ppm NO2 at 500 °C, which is significantly better than commercial YSZ sensor. This work makes a significant progress in solid electrolytes and gas sensor.

Structural, optical and electronic properties of RFeO3

Effect of R site ionic radius on the structural, optical and electronic properties of rare-earth orthoferrites (RFeO3) (where, R = La, Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, and Yb) have been investigated experimentally and theoretically. Synchrotron-based X-ray diffraction studies followed by Rietveld refinement confirmed that the lattice constants, R–O bond length and Fe–O–Fe bond angle increase systematically, whereas the Fe–O bond length (i.e. overlap between O-2p and Fe-3d orbitals) associated with FeO6 octahedra almost remains constant throughout RFeO3 series. The energy bandgap (Eg) of all the samples have been measured using optical absorption spectroscopy and the same is found between ~ 1.94 and 1.97 eV, i.e. Eg almost remains constant throughout RFeO3 series. First principle DFT analysis confirmed that the “density of states” near Fermi level in all the studied samples is dominated by O-2p and Fe-3d orbitals. Thus, it appears that the constant value of Fe–O bond length (i.e. Fe-O overlap) associated with FeO6 octahedra might be responsible for the constant value of band gap in these samples.

Effect of different RE site ionic radii on the electronic structures and elastic properties of Ba2RENbO6: A first-principles study

RE site ionic radius has a critical influence on the properties of double perovskite oxide Ba2RENbO6. In this paper, the electronic structures and elastic properties of Ba2RENbO6 (RE = Ho, Er, Yb) have been calculated by using the plane-wave pseudopotential density functional theory, and the effect of the different RE site ions on the structures and properties of Ba2RENbO6 is discussed. Results indicate that Ba2RENbO6 (RE = Ho, Er, Yb) are all direct bandgap semiconductors with a bandgap of 0.95 eV, 1.26 eV and 2.36 eV, respectively. With the decrease of the RE site ionic radius of Ba2RENbO6 (RE = Ho, Er, Yb), RE–O and Nb–O covalent bonds are enhanced, and the elastic constants ([Formula: see text], [Formula: see text], [Formula: see text]), elastic modulus ([Formula: see text], [Formula: see text], [Formula: see text]), [Formula: see text], Poisson’s ratio ([Formula: see text]), the Debye temperature [Formula: see text], Gruneisen parameters [Formula: see text] all show a trend of increase. The elastic and thermodynamic properties are all improved with the decreasing radius of RE site ion.

Magneto-orbital ordering in the divalent A -site quadruple perovskite manganites AMn7O12 ( A=Sr , Cd, and Pb)

Through analysis of variable temperature neutron powder diffraction data, we present solutions for the magnetic structures of SrMn$_7$O$_{12}$, CdMn$_7$O$_{12}$, and PbMn$_7$O$_{12}$ in all long-range ordered phases. The three compounds were found to have magnetic structures analogous to that reported for CaMn$_7$O$_{12}$. They all feature a higher temperature lock-in phase with \emph{commensurate} magneto-orbital coupling, and a delocked, multi-\textbf{k} magnetic ground state where \emph{incommensurate} magneto-orbital coupling gives rise to a constant-moment magnetic helix with modulated spin helicity. CdMn$_7$O$_{12}$ represents a special case in which the orbital modulation is commensurate with the crystal lattice and involves stacking of fully and partially polarized orbital states. Our results provide a robust confirmation of the phenomenological model for magneto-orbital coupling previously presented for CaMn$_7$O$_{12}$. Furthermore, we show that the model is universal to the $A^{2+}$ quadruple perovskite manganites synthesised to date, and that it is tunable by selection of the $A$-site ionic radius.

A-site cationic disorder induced significantly large magnetoresistance in polycrystalline La0.2Gd0.5Ba0.3MnO3 compound

The observation of significantly large magnetoresistance at the liquid nitrogen temperature range in the polycrystalline La0.2Gd0.5Ba0.3MnO3 (LGBMO) compound has been addressed in the present manuscript. The motivation of considering LGBMO sample is the average ‘A’ site ionic radius 〈rA〉 and tolerance factor (t), almost same as that of La0.7Sr0.3MnO3 (LSMO), which is a well studied colossal magnetoresistive material. Magnetoresistance of the LGBMO compound has been compared with the LSMO as well as parent compound La0.7Ba0.3MnO3(LBMO) to show the enhancement of magnetoresistance in LGBMO compound. This observed nature has been elucidated considering the disorder induced short range magnetic interaction due to the enhance size disorder parameter (σ2). Our study revels that, size disorder parameter plays the crucial role for enhancing the colossal magnetoresistance.

Alteration of magnetic behavior and microstructural distortion of EuMnO3 by partial substitution of Eu with monovalent Na

Effect of monovalent sodium doping on inherent lattice distortion and magnetic properties of EuMnO3 is reported in this work. Perovskite structured Eu1-xNaxMnO3 (x = 0.0, 0.1, 0.2) compounds are prepared by conventional sol-gel method. Inherent structural distortion of EuMnO3 and its modification by Na doping is investigated by analyzing powder X-ray diffraction patterns of these compounds. Numerical values of different structural and microstructural parameters related to structural distortion are evaluated by Rietveld analysis of XRD patterns. Different distortions in MnO6 octahedra are shown by 3D atomic models. The value of Goldschimdt tolerance factor is calculated as 0.8711 for the undoped compound and 0.8870 and 0.8856 for the 10mol% and 20mol% Na doped compounds respectively. Na doping stabilizes the orthorhombic perovskite structure and reduces both octahedral and Jahn-Teller distortion by increasing the average R site ionic radii and by introducing non Jahn-Teller Mn+4 ions in the compound. Magnetic behaviors of the compounds are studied by temperature dependent magnetization measurement. Anti-ferromagnetic EuMnO3 with Neel temperature 33 K transforms to ferromagnetic Eu1-xNaxMnO3 with Curie temperature 42.5 K and 42.9 K for10 and 20mol% Na doping respectively. However, 10mol% Na doping found to be more effective than 20mol% for stabilization of structure and reduction of octahedral distortion as well as in introducing ferromagnetic ordering.

Probing structural distortions in rare earth chromites using Indian synchrotron radiation source

Effect of R site ionic radius on the structural distortions in RCrO3 (R: La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y) rare earth perovskite chromites is investigated through synchrotron based X-ray diffraction technique. The said structural distortions are measured in the terms of CrO bond lengths, CrO6 octahedral tilt, tolerance factor (t) and RO12 polyhedral distortion. It is observed that the lattice parameters (b and c), RO bond length, tolerance factor and Cr–O–Cr bond angle increases with increase in the radius of R site ion; whereas octahedral tilts (along [010] and [101]) and RO12 polyhedral distortion decreases with increase in the radius of R site ion. Further it is observed that the radius of R site cation does not have significant effect on lattice parameter ‘a’ and CrO bond length (hence on the distortion of CrO6 octahedra). A comparison of the crystal structure parameters obtained using refinement of synchrotron powder X-ray data and that estimated theoretically using modern bond valence parameters (SPuDS) has been carried out. A one to one correlation between the experimental and theoretical results has been observed.

Characterization, structural and magnetic properties of the as-prepared Mg-substituted Cu-nanoferrites

The as-prepared Cu1−xMgxFe2O4 nanoferrites, 0⩽x⩽1, were synthesized using the co-precipitation method. The samples were characterized using the X-ray diffraction, transmission electron microscopy, infrared (IR) and Mössbauer spectroscopy and vibrating sample magnetometer. This study proved that the samples have single-phase cubic spinel structure, nanometric size and superparamagnetic behavior. The nanoparticle and crystallite size (R) showed a dependence on the Mg ion content x. The Mössbauer spectra were analyzed and assigned to two magnetic subpatterns and/or two quadrupole doublets due to Fe ions among the tetrahedral A-sites and octahedral B-sites. Six IR absorption bands were observed and assigned to the corresponding vibration modes. The saturation magnetization showed decrease against x and proved dependence on R. The lattice constant, hopping lengths, strain, site characteristic bands and B-site force constant showed x dependence, whereas oxygen parameter and A-site force constant did not. The site ionic radii and edges, density, porosity, Debye temperature, stiffness constant, hyperfine interaction and magnetic parameters were deduced and discussed as functions of x and the cation distributions were estimated.

Cation distribution controlled dielectric, electrical and magnetic behavior of In3+ substituted cobalt ferrites synthesized via solid-state reaction technique

We report the structural, cation distribution, dielectric, electrical and magnetic properties of CoFe2−xInxO4 (0.0 ≤ x ≤ 0.6) ferrites. Rietveld fitted X-ray diffraction (XRD) patterns confirm the formation of single phase cubic spinel structure with Fd3m space group for all the samples. The comprehensive analysis of XRD based cation distribution has been performed to see the effect of In3+ ions substitution on various structural parameters such as site ionic radii, edge and bond lengths, interionic distances etc. The dielectric constant and tangent loss have been studied as a function of temperature and frequency. The dielectric data presented in electric modulus form reveals the presence of non-Debye relaxation behavior in considered ferrites. Both the AC and DC conductivities as a function of temperature are found to decrease with increasing In3+ content. The power law behavior of AC-conductivity indicates a strong correlation among electrons in these systems. The isothermal magnetization versus applied field curves with high field slope and significant coercivity suggest that studied materials are highly anisotropic with canted spin structures and exhibit ferrimagnetic behavior at 300 K. Magnetization gets enhanced up to 40% of In3+ substitution. The observed low dielectric losses and high resistivity can find their application in power transformers at high frequencies.

Thermopower studies of rare earth doped lanthanum barium manganites

Influence of rare earth doping on electrical, magnetic and thermopower studies of La0.34Re0.33Ba0.33MnO3 compound was investigated. Ferro to paramagnetic transition and metal to insulator transition temperatures decrease with decreasing ionic radius of the dopant ion. Electrical resistivity in the entire temperature range is explained by phase separation model. The magnitude of Seebeck coefficient increases with increasing dopant ionic radius. A cross over from negative to positive sign has also been observed in thermopower data with decreasing A site ionic radius (〈rA〉). The low temperature thermopower data has been explained using a qualitative model containing diffusion; magnon drag and phonon drag effects while the paramagnetic insulating part has been analyzed using small polaron hopping mechanism.

Effect of Al3+ substitution on structural, cation distribution, electrical and magnetic properties of CoFe2O4

We present the structural, cation distribution, electrical and magnetic studies of CoAlxFe2−xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8) ferrites. The Rietveld-fitted X-ray diffraction (XRD) patterns confirm the formation of single-phase cubic spinel structures with Fd3¯m space group for all the samples. A comprehensive analysis of XRD-based cation distribution has been performed to see the effect of Al3+ ions substitution on various structural parameters such as site ionic radii, edge length, bond length and interionic distances. The dielectric constant and direct current (DC) conductivity decreases with increasing Al3+ substitution up to x = 0.4. However, with further increase in Al3+ substitution, both the dielectric constant and the DC conductivity increase. The presentation of dielectric data in the complex electric modulus form reveals the presence of a non-Debye-type relaxation behaviour in the considered ferrites. The power law behaviour of alternating current (AC) conductivity indicates a strong correlation among electrons in these systems. The isothermal magnetisation versus applied field curves with high-field slope and significant coercivity suggest that the studied materials are highly anisotropic with canted spin structures. The samples exhibit ferrimagnetic behaviour at 300K and the magnetisation decreases with increasing Al3+ concentration. The as-prepared samples are promising candidates for various industrial applications.

The Effect off–dMagnetic Coupling in MultiferroicRMnO3Crystals

We have established detailed magnetoelectric phase diagrams of (Eu$_{0.595}$Y$_{0.405}$)$_{1-x}$Tb$_x$MnO$_3$ ($0 \le x \le 1$) and (Eu,Y)$_{1-x}$Gd$_x$MnO$_3$ ($0 \le x \le 0.69$), whose average ionic radii of $R$-site ($R$: rare earth) cations are equal to that of Tb$^{3+}$, in order to reveal the effect of rare earth 4$f$ magnetic moments on the magnetoelectric properties. In spite of the same $R$-site ionic radii, the magnetoelectric properties of the two systems are remarkably different from each other. A small amount of Tb substitution on $R$ sites ($x \sim 0.2$) totally destroys ferroelectric polarization along the a axis ($P_a$), and an increase in Tb concentration stabilizes the $P_c$ phase. On the other hand, Gd substitution ($x \sim 0.2$) extinguishes the $P_c$ phase, and slightly suppresses the $P_a$ phase. These results demonstrate that the magnetoelectric properties of $R$MnO$_3$ strongly depend on the characteristics of the rare earth 4$f$ moments.

Vacancy induced spin state transition in La0.7Sr0.3-x□xCoO3 (0≤x≤0.2) cobaltites

Effects of vacancy doping in polycrystalline La0.7Sr0.3-xxCoO3 (0≤x≤0.2) cobaltites on their crystal structure, magnetic and transport properties have been systematically investigated. With increasing Sr deficiency, the antiferromagnetic superexchange is promoted at the expense of double exchange between ferromagnetic clusters, with cluster-glass state being prevailing, which is due to the gradual decrease of A site ionic radius as well as more intrinsic disorder. As x is increased beyond 0.1, it is found that the Co—O bond length shrinks remarkably. This tends to enlarge the crystal-field splitting energy and most Co3+ ions are inclined to prefer low spin states. The ground state shows superparamagnetic-like features, thus giving rise to metal-insulator transition.

Electron-phonon interactions in perovskites containing Fe and Cr studied by Raman scattering using oxygen-isotope and cation substitution

We use temperature-dependent inelastic light scattering to study the origin of the strong multiphonon scattering of a local oxygen breathing mode present in the mixed $B$-site orthorhombic (space group $Pnma$) perovskite ${\text{LaFe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$ but absent in isostructural ${\text{LaFeO}}_{3}$ and ${\text{LaCrO}}_{3}$. It is seen that the multiphonon scattering is critically sensitive to the presence of both Fe and Cr ions on the $B$ site. These results support our interpretation that the multiphonon scattering is activated by local electron-phonon interactions according to the Franck-Condon picture following an Fe-Cr charge transfer. Further, $^{18}\text{O}$ substitution is performed on the $x=0$, 0.04, and 0.5 compounds and clearly shows that all modes appearing above the first-order phonon-scattering region in these compounds originate from higher-order oxygen stretching vibrations. In particular this is the case for the strong second-order scattering dominating the scattering response in ${\text{LaFeO}}_{3}$. Accordingly we propose that these modes are generated by infrared-active longitudinal optical (IR LO) two-phonon and combination scattering activated by Fr\ohlich interaction. For $x=0.02$ and 0.04 the characteristic IR LO two-phonon and Franck-Condon multiphonon-scattering profiles mix. We also study the influence of isovalent cation substitution and Sr doping in $A{\text{Fe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$ ($A=\text{La}$, Nd, and Gd) and ${\text{La}}_{1\ensuremath{-}y}{\text{Sr}}_{y}{\text{Fe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ ($y=0$, 0.16, and 0.5) on the strong electron-phonon coupling present in ${\text{LaFe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$. The Franck-Condon effect in ${\text{LaFe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$, is not significantly affected by isovalent $A$-site substitution, despite the increasing orthorhombic distortion associated with decreasing $A$-site ionic radii. On the contrary, aliovalent Sr doping causes a rapid decrease in the Franck-Condon scattering. This shows that the strong electron-phonon coupling in these compounds is highly sensitive to local lattice and electronic decoherence but insensitive to global lattice distortions. Finally, a preliminary assignment of the ${A}_{g}$ and ${B}_{2g}$ phonon modes in $A{\text{Fe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$ ($A=\text{La}$, Nd, and Gd) is made based on the present observations and published results for ${\text{LaCrO}}_{3}$ and $A{\text{MnO}}_{3}$. The modes associated with oxygen octahedral tilt and bending vibrations are heavily influenced by the magnitude of the orthorhombic distortion.

Effect of Cation Substitution and Non‐Stoichiometry on the Microwave Dielectric Properties of Sr(B′0.5Ta0.5)O3 [B′=Lanthanides] Perovskites

The Sr(B′0.5Ta0.5)O3 ceramics where B′=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, and Yb have been prepared by the conventional solid‐state ceramic route and their microwave dielectric properties have been investigated. The structure and microstructure of the ceramics have been characterized by X‐ray diffraction and scanning electron microscope techniques. The relative permittiviy (ɛr) varies linearly with B′‐site ionic radii, except for La, and the temperature coefficient of resonant frequency (τf) varies linearly with the tolerance factor. The Sr(B′0.5Ta0.5)O3 ceramics have ɛr in the range 25.9–32, Qu×f=4500–54 300 GHz, and τf=−79 to −42 ppm/°C. A slight deviation from stoichiometry affects the dielectric properties of these double perovskites. Partial substitution of Ba for Sr could tune the dielectric properties. Addition of rutile (TiO2) lowered the sintering temperature and improved the dielectric properties of Sr(B′0.5Ta0.5)O3 ceramics.

Structural and magnetic properties ofLa1−xPrxMnO3+δ(0⩽x⩽1.0)

X-ray, neutron powder diffraction (NPD), and magnetic measurements were performed in order to investigate the effect of Pr substitution for La on crystallographic structure, on character of magnetic ordering, and on transition temperature in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3+\ensuremath{\delta}}$ manganites series $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}1.0)$. Strong dependence of structural and magnetic properties on average $A$-site ionic radius was found. The magnetic phase diagram, characterizing Pr concentration dependence of the phase transition temperature, was constructed, based on magnetic and on NPD results. In the compounds with $xl0.7$, the ferromagneticlike behavior with ferromagnetic moment aligned along the $b$ axis was observed in the temperature interval below the Curie temperature, ${T}_{\mathrm{C}}$, varying in the range of $113--153\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, down to Mn ions canted spin arrangement transition temperature, ${T}_{\mathrm{CANT}}$, varying in the range of $73--115\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. It was found that ${T}_{\mathrm{C}}$ changes nonmonotonously with Pr content, it decreases rapidly for $xl0.3$ and for $xg0.6$, while is practically independent on $x$ for $0.3lxl0.6$. The Mn magnetic moments increase from 3.2 for $x=0$ to 3.6 for $x=0.3$ before decreasing to $1.7\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}∕\mathrm{Mn}$ for $x=1.0$ and form a canting structure with canting angle decreasing from 32\ifmmode^\circ\else\textdegree\fi{} for $x=0$ to 16\ifmmode^\circ\else\textdegree\fi{} for $x=0.3$ and then increasing to 70\ifmmode^\circ\else\textdegree\fi{} for $x=1.0$. The NPD and x-ray diffraction data indicate that Pr doping in $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3}$ is accompanied by changes of both the lattice parameters and crystal structure. The compound with $x=0$ was shown to have a rhombohedral crystal structure, while the samples with $0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}0.6$ have orthorhombic symmetry with a small Jahn-Teller distortion (or pseudocubic) which continuously transforms towards highly distorted orthorhombic structure for $xg0.6$. From ac magnetic susceptibility, studied under hydrostatic pressure up to $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, it was found that ${T}_{\mathrm{C}}$ and ${T}_{\mathrm{CANT}}$ change linearly with an applied pressure. The results are interpreted taking into account the competition of ferromagnetic double-exchange and antiferromagnetic superexchange interactions. This competition leads to a low temperature disordered system with spin canted features as a result of a decrease of the average $A$-site cation radius followed by decrease of Mn-O bond lengths, Mn-O-Mn bond angles, and the static Jahn-Teller distortion of the $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra.

Dimensional Crossover in Transport Property in Manganite Thin Films with Finely Controlled Lattice Distortion

We have investigated the effect of Jahn–Teller-type distortion in manganite thin films with finely controlled lattice distortion by exploiting epitaxial strain effect and tuning A -site ionic radius. The magnetic and transport properties of these films indicate the existence of the dimensional crossover in conduction as the lattice distortion changes. We also found a universal relationship between magnetization and resistivity irrespective of the sample compositions.

Structural properties of magnesium and aluminium co-substituted lithium ferrite

The structural properties of Mg2+ and Al3+ co-substituted Li0.5Fe2.5O4 are studied by synthesizing the spinel solid solution series MgxAl2xLi0.5(1−x)Fe2.5(1−x)O4. Polycrystalline samples of this series with x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 have been prepared by double-sintering ceramic method. The structural details like: lattice constant and distribution of cations in the tetrahedral and octahedral interstitial voids have been deduced through X-ray diffraction (XRD) data analysis. The x dependence of bond length, oxygen positional parameter, site ionic radii, bulk density, porosity and shrinkages have also been determined.