Orthorhombic Distortion Research Articles

Electrical conductivity of YBa2Cu3O7-δ single crystals under conditions of anionic ordering in Cu(1)O1-δ layers

The influence of thermocycling annealing processes on the oxygen ordering degree (order parameter) in YBa2Cu3O7-δ single crystals has been studied. It has been shown that an increase in the critical onset temperature of the transition to the superconducting state during thermocycling annealing procedures is consistent with the decrease of the σс/σаb parameter. This fact indicates a redistribution of the electronic density between the structurally inhomogeneous Cu(2)O2 and Cu(1)O1-δ planes, due to the formation of oxygen long-range order in the O(4)–Cu(1)–O(4) linear groups along the (b) crystal structure axis of the unit cell, and elimination of oxygen defects in the square nets of the Cu(2)O2 planes. The existence of the critical value of the conductivity anisotropy σс/σаb, below which its behavior does not correlate with the change of Тс, has been confirmed. In this case an increase in Тс and orthorhombic distortion of the crystal structure during isothermal annealing are caused by the amplification of the “interlayer” interaction between the Cu(2)О2 and Cu(1)О1-δ planes. As a result, the contribution of the Cu(1)О1-δ chain layers to the electron state density at the Fermi level increases. These layers can acquire superconducting properties due to tunneling of Cooper pairs from the Cu(2)О2 planes resulting in the formation of the induced superconductivity in these planes.

Electrical conductivity of YBa2Cu3O7-δ single crystals under conditions of anionic ordering in Cu(1)O1-δ layers

The influence of thermocycling annealing processes on the oxygen ordering degree (order parameter) in theYBa2Cu3O7-δ single crystals have been studied. It was determined that an increase in the critical temperature of the onset of the transition to the superconducting state during step annealing procedures is consistent with decrease of the σс/σаb parameter. This fact indicates the redistribution of the electronic density between the Cu(2)O2 and Cu(1)O1-d structurally-inhomogeneous planes, due to the formation of the oxygen long-range ordering in the O(4)—Cu(1)—O(4) linear groups along the (b) crystal structure axis of the unit cell, and removal of the oxygen defects in the square nets of the Cu(2)O2 planes. The existence of a critical value of the conductivity anisotropy σс/σаb, below which its behavior does not correlate with the change of Тс, has been proved. In this case, the increase of Тс and the orthorhombic distortion of the crystal structure at the isothermal annealing processes occur due to the amplification of the «interlayer» interaction between the Cu(2)О2 and Cu(1)О1-δ planes. As a result, the contribution of the Cu(1)О1-δ chain layers in the electronstate density on the Fermi level increases. These layers could be the superconducting ones by means of the Cooper pairs tunneling from the Cu(2)О2 planes, forming the induced superconductivity there.

Influence of rare-earth doping on the structural and dielectric properties of orthoferrite La0.50R0.50FeO3 ceramics synthesized under high pressure

Abstract The effect of co-doping on the structural and dielectric properties of the La0.50R0.50FeO3 orthoferrites for a full number of substitutions (R = Ce–Lu) has been experimentally and theoretically studied using X-ray diffraction, SEM, EDS, and dielectric spectroscopy methods. The La0.50R0.50FeO3 ceramics with R = Nd, Sm, Gd, Dy, and Er, prepared by a solid-state reaction method under cold pressing at high pressure P = 4 GPa, have been taken as a basis. Structural parameters in the La0.50R0.50FeO3 orthoferrites have been obtained using Rietveld refinement of X-ray experimental data with their further approximation by linear dependence. Monotonic change in crystal lattice parameters, orthorhombic distortion degree, global instability index, and Goldschmidt tolerance factor have been observed for all samples doped by different R-cations. With increase in the radius of R-cation, a growth in an average grain size has been detected. The investigation of dielectric properties in a wide frequency range of 10−1–1010 Hz and their theoretical description with determining main mechanisms of dielectric polarization made it possible to establish regularities among a type of doping R-cation, crystal-chemical parameters and dielectric properties. The studied ceramic La0.50R0.50FeO3 samples demonstrate colossal dielectric constant ∼ 104 and relatively small dielectric loss tangent in a low-frequency range. The obtained results can be useful for further application of orthoferrite-based materials as sensor and switching devices.

Investigation of alteration in physical properties of dysprosium orthochromite instigated through cobalt doping

Abstract We report the systematic investigations on DyCr1–xCoxO3 (0 ≤ x ≤ 0.3) samples prepared through sol-gel auto combustion process. Rietveld refinement of the powder x-ray diffraction patterns assures the formation of mono-phase orthorhombic structure with space group Pbnm. In order to get an obvious view about the effect of substitution of Cr3+ with Co3+ ions on crystallographic parameters of these samples, the tilt angles, cell and orthorhombic distortions were calculated. The average crystallite sizes and lattice strain as computed from the Williamson-Hall analysis are found to rise with the increase in Co content. The porosity of the synthesized samples lies in between ∼30 and 38%. The Fourier transform infrared (FTIR) spectra of these samples affirm the formation of desired crystal structure. Field emission scanning electron microscopy (FESEM) images exhibit the existence of polycrystalline microstructure. The energy dispersive x-ray (EDX) analysis assures the elemental compositions of the prepared samples. UV/Visible spectroscopy is utilized to estimate the energy band gap, Urbach energy and threshold wavelength. The energy band gap reduces whereas Urbach energy and threshold wavelength enhance on increasing the cobalt content. Dielectric responses of these samples have been analysed in view of “universal dielectric response” model. AC conductivity increases with the increase in frequency and that affirm the small polaron hopping type of conduction mechanism in the investigated frequency range. The relaxation peaks appear in imaginary part of impedance spectra shift toward lower frequencies with the increase in Co concentration which indicates the higher values of relaxation time in the doped samples. Differential thermal analysis reveals the structural transitions and improved thermal stability of the Co doped samples.

Structural distortions in rare-earth transition-metal oxide perovskites under high pressure

Owing to their structural complexity and wide range of possible chemical combinations, perovskite oxides exhibit many technically important physical properties. Pressure is a thermodynamic parameter which is useful for tuning physical properties; however, the response of the complex crystal structure to high pressure has not been thoroughly studied and rationalized. This study focuses on in situ high-pressure x-ray diffraction of the orthorhombic perovskite oxides ${A}^{3+}{B}^{3+}{\mathrm{O}}_{3}$, commonly found for the rare-earth transition-metal oxides of the $RM{\mathrm{O}}_{3}$ formula. Each of the four families of $RM{\mathrm{O}}_{3}$ ($M=\mathrm{Ti}$, Cr, Mn, Fe) perovskites in this study all crystallize in the same orthorhombic perovskite structure with the Pbnm space group. The lanthanide contraction in these materials leads to varying degrees of orthorhombic distortions that are primarily associated with octahedral site rotations. The pressure-induced change of the lattice parameters demonstrates an evolution from a suppression to an enlargement of the orthorhombic distortion for substitution of the rare-earth element from $R=\mathrm{La}$ to Lu in $RM{\mathrm{O}}_{3}$ perovskites. This unusual crossover of the lattice parameters' dependence on pressure contradict the results from first-principles calculation but can be rationalized by the intrinsic distortion of the perovskite structure.

Anomalous pressure dependence of the electronic transport and anisotropy in SrIrO3 films

Iridate oxides display exotic physical properties that arise from the interplay between a large spin–orbit coupling and electron correlations. Here, we present a comprehensive study of the effects of hydrostatic pressure on the electronic transport properties of SrIrO3 (SIO), a system that has recently attracted a lot of attention as potential correlated Dirac semimetal. Our investigations on untwinned thin films of SIO reveal that the electrical resistivity of this material is intrinsically anisotropic and controlled by the orthorhombic distortion of the perovskite unit cell. These effects provide another evidence for the strong coupling between the electronic and lattice degrees of freedom in this class of compounds. Upon increasing pressure, a systematic increase of the transport anisotropies is observed. The anomalous pressure-induced changes of the resistivity cannot be accounted for by the pressure dependence of the density of the electron charge carriers, as inferred from Hall effect measurements. Moreover, pressure-induced rotations of the IrO6 octahedra likely occur within the distorted perovskite unit cell and affect electron mobility of this system.

Unexpected crystalline homogeneity from the disordered bond network in La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 films

Designing and understanding functional electronic and magnetic properties in perovskite oxides requires controlling and tuning the underlying crystal lattice. Here we report the structure, including oxygen and cation positions, of a single-crystal, entropy stabilized perovskite oxide film of La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 grown on SrTiO3 (001). The parent materials range from orthorhombic (LaCrO3, LaMnO3 and LaFeO3) to rhombohedral (LaCoO3 and LaNiO3), and first principles calculations indicate that these structural motifs are nearly degenerate in energy and should be highly distorted site-to-site. Despite this extraordinary local configurational disorder on the B-site sublattice, we find a structure with unexpected macroscopic crystalline homogeneity with a clear orthorhombic unit cell, whose orientation is demonstrated to be controlled by the strain and crystal structure of the substrate for films grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) and NdGaO3 (110). Furthermore, quantification of the atom positions within the unit cell reveal that the orthorhombic distortions are small, close to LaCrO3, which may be driven by a combination of disorder averaging and the average ionic radii. This is the first step towards understanding the rules for designing new crystal motifs and tuning functional properties through controlled configurational complexity.

Synthesis and structural studies of novel aminopolychloroethylated chelate acetylacetonate complexes of aluminum (III) and chromium (III)

Novel bio-medicinally promising complexes of amidotrichloroethylated acetylacetonate with Cr(III) and Al(III), which combine synthetically and pharmacologically attractive fragments, have been synthesized. Structural peculiarities of the complexes were investigated by magnetic resonance techniques (EPR, NMR) and some other modern physical-chemical methods (FT-IR, SEM, and elemental analysis). The axial and orthorhombic distortions of octahedral symmetry are observed in the acetylacetonate derivatives due to the presence of structurally different acetylacetonate ligands in the coordination medium that is supported by EPR and X-ray diffraction analysis data.

Phase relation studies in the CeO2–La2O3–Er2O3 system at 1500°C

Materials based on CeO2–La2O3–Er2O3 system are promising candidates for a wide of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the isothermal section of the phase diagram for 1500 °C was investigated. The phase relations in the CeO2–La2O3–Er2O3 ternary system at 1500 °C were studied by X-ray diffraction and scanning electron microscopy in the overall concentration range. To study phase relationships at 1500 °C the as-repared samples were thermally treated in two stages: at 1100 °C (for 300 in air) and then at 1500 °C (for 70 h in air) in the furnaces with heating elements based on Fecral (H23U5T) and Superkanthal (MoSi2), respectively. The solid solutions based on various polymorphous forms of constituent phases and with perovskite-type structure of LaErO3 (R) with orthorhombic distortions were revealed in the system. No new phases were found. The isothermal section of the phase diagram for the CeO2–La2O3–Er2O3 system has been constructed. It was established that in the ternary CeO2–La2O3–Er2O3 system there exist fields of solid solutions based on hexagonal (A) modification of La2O3, cubic modification of CeO2 with fluorite-type structure (F), cubic modification Er2O3 and with perovskite-type structure of LaErO3 (R) with orthorhombic distortions. The maximal solubility of ceria in LaErO3 was found to be around ∼ 2 mol% CeO2 along the section CeO2–(50 mol % La2O3 –50 mol% Er2O3).

Effect of grain interior and grain boundaries on transport properties of Sc-doped CaHfO3

Abstract A novel CaHf0.9Sc0.1O3-α perovskite protonic conductor was prepared and the effects of grain interior and grain boundaries on the carriers’ transport properties were systematically investigated via defect chemistry theory and H2/H2O concentration cell. The CaHf0.9Sc0.1O3-α exhibited an orthorhombic distortion and the standard molar hydration enthalpy of CaHf0.9Sc0.1O3-α was found to be −44 kJ/mol. The migration activation energies for conduction of protons, oxygen vacancies, and holes in CaHf0.9Sc0.1O3-α under oxygen were 0.81 eV, 1.68 eV, and 1.79 eV, respectively. The proton concentration in CaHf0.9Sc0.1O3-α grains was higher than that in the grain boundaries, while in contrast, the oxygen vacancy concentration in grains was lower than that in the grain boundaries. The proton conduction through CaHf0.9Sc0.1O3-α was dominant in Ar as well as reductive atmospheres at 500–800 °C, where the hole conductivity ( σ h · ) and hole transport number ( t h · ) remarkably increased with increasing oxygen partial pressure. The relative transport number results reveal that the grain interior of CaHf0.9Sc0.1O3-α is better suited than grain boundaries to block the hole transport, and grains interior could be used to improve the protons transport number t OH O · .

Structural and Electrical Properties of Ca2+ Doped LaFeO3: The Effect of A-site Cation Size Mismatch

In this study, nanosized La1-xCaxFeO3 (0.00≤x≤0.40) compounds prepared via sol-gel method followed by heat treatment at 1100oC for 24 hours are studied. Crystal structure, microstructure, surface morphology and temperature-dependent resistivity of the samples are investigated. TEM investigation reveals nanoparticles with an average size of 35nm produced from the sol-gel process. The crystal structure of the compounds belongs to an orthorhombically distorted perovskite structure with Pbnm space group. Lattice distortion and cation size mismatch increase with an increase in Ca and particle and grain growth are suppressed by Ca doping. Electrical conduction is explained via thermally activated hopping of small polarons. Unit cell volume, charge ordering temperature, and activation energy for small polarons decrease linearly with an increase in cation size mismatch. Room temperature resistivity decreases with Ca doping and gets its minimum value for 30% Ca at which the orthorhombic distortion is maximum.

Dielectric properties of sodium and neodymium substitute to A-Site SrBi4Ti4O15 ceramics

Polycrystalline ceramics, SrBi4Ti4O15 (SBT) and Sr0.2Na0.4Nd0.4Bi4Ti4O15 (SNBT), were synthesized by solid state sintering method using planetary ball mill. The stoichiometric powders were ground for 10 hours. Single phase formation was established from the XRD results. The highest peak (119) was seen at 30°. X-ray diffraction results indicated decreased cell volume and orthorhombic distortion with the substitution of Na+ and Nd3+ in place of Sr2+. The lattice parameters were measured using Unitcell software. Grain size as well as grains random orientation was observed from scanning electron microscope results. Dielectric properties were measured using Novo control dielectric analyzer, from room temperature to 1200 °C at frequencies 1 kHz, 10 kHz, 50 kHz, 100 kHz, 500 kHz, and 1 MHz. The dielectric constant and loss decreased whereas the Curie temperature increased when Na+ and Nd3+ were substituted to A- site in SBT. This ceramic has enhanced thermal stability thus making this ceramic appropriate for sensor applications at high temperatures.

Controlled-Atmosphere Sintering of KNbO3

The effect of sintering atmosphere (O2, air, N2, N2-5% H2, and H2) on the densification, grain growth, and structure of KNbO3 was studied. KNbO3 powder was prepared by solid state reaction, and samples were sintered at 1040 °C for 1–10 h. The sample microstructure was studied using Scanning Electron Microscopy (SEM). The sample structure was studied using X-Ray Diffraction (XRD). H2-sintered samples showed reduced density, whereas other sintering atmospheres did not affect density much. Samples sintered in N2-5% H2 showed abnormal grain growth, whereas sintering in other atmospheres caused stagnant (O2, air, N2) or pseudo-normal (H2) grain growth behavior. Samples sintered in reducing atmospheres showed decreased orthorhombic unit cell distortion. The grain growth behavior was explained by the mixed control theory. An increase in vacancy concentration caused by sintering in reducing atmospheres led to a decrease in the step free energy and the critical driving force for appreciable grain growth. This caused grain growth behavior to change from stagnant to abnormal and eventually pseudo-normal.

Structural and electrical effects of Ag substitution in tungsten bronze Sr2AgxNa1−xNb5O15 ceramics

In this work, the correlation between the composition and structure of the Sr2AgxNa1−xNb5O15 (SANN, 0.00 ≤ x ≤ 1.00) ferroelectric ceramic was investigated. The SANN ceramic was synthesized via the solid-state reaction method and equivalently charged Ag+ cations were doped in the SANN matrix to investigate the relationship between the composition and structure. Investigation of the ceramic's properties mainly focused on two aspects: (1) enhancement of the dielectric and ferroelectric properties caused by the dense structure, increased orthorhombic distortion, and increased disorder distribution; (2) the low-temperature dielectric anomaly evolved from a slightly smeared out phase transition into an obvious ferroelastic/ferroelectric phase transition by Ag+ introduction in SANN. In addition, improved light transmittance was realized at x = 1.00, which may be related to the homogeneous equiaxed microstructure and uniform size of the ceramic grains.

Scaling behavior of low-temperature orthorhombic domains in the prototypical high-temperature superconductor La1.875Ba0.125CuO4

Translational/rotational symmetry breaking and recovery in condensed matter systems are closely related to exotic physical properties such as superconductivity (SC), magnetism, spin density waves (SDW) and charge density waves (CDW). The interplay between different order parameters is intricate and often subject to intense debate, as in the case of CDW order and superconductivity. In La1:875Ba0:125CuO4 (LBCO), the locations of CDW domains are found to be pinned on the nanometer size scale. Coherent X-ray diffraction techniques open routes to directly visualize the domain structures associated with these symmetry changes. We have pushed Bragg Coherent Diffractive Imaging (BCDI) into the cryogenic regime where most phase transitions in quantum materials reside. Utilizing BCDI, we image the structural evolution of LBCO microcrystal samples during the high-temperature-tetragonal (HTT) to low-temperature-orthorhombic (LTO) phase transition. Our results show the formation of LTO domains close to the transition temperature and how the domain size varies with temperature. The LTO domain size is shown to decrease with temperature and to be inversely proportional to the magnitude of the orthorhombic distortion. The number of domains follows the secondary order parameter (or orthorhombic strain) measurement with a critical exponent that is consistent with the 3D universality class.

Uniaxial c -axis pressure effects on the underdoped superconductor BaFe2(As0.72P0.28)2

The optimal superconductivity ($T_c \approx 30 $ K) in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ can be reached when the coupled antiferromagnetic (AF) order ($T_N$) and orthorhombic lattice distortion ($T_s$) are suppressed to zero temperature with increasing of P concentration or hydrostatic pressure. Here we use transport and neutron scattering to study the $c$-axis pressure effects on electronic phases in underdoped BaFe$_2$(As$_{0.72}$P$_{0.28}$)$_2$, which has $T_N = T_s\approx 40$ K and $T_c \approx $ 28 K at zero pressure. With increasing $c$-axis pressure, $T_N$ and $T_s$ are slightly enhanced around $P_c \sim 20 $ MPa. Upon further increasing pressure, AF order is gradually suppressed to zero, while $T_c$ is enhanced to 30 K. Our results reveal the importance of magnetoelastic couplings in BaFe$_2$(As$_{1-x}$P$_x$)$_2$, suggesting that the $c$-axis pressure can be used as a tuning parameter to manipulate the electronic phases in iron pnictides.

Indium doping in SrCeO3 proton-conducting perovskites

In this work we present results of studies of In3+ doping in strontium cerate, comprising structural aspects, and oxygen as well as proton conductivity. Crystal structure analysis of single-phase SrCe1-xInxO3-a (x ​= ​0.1, 0.2 and 0.3) materials in 25–900 ​°C temperature range indicates presence of strong orthorhombic distortion of the perovskite-type structure, similar as for the undoped SrCeO3. Limited sinterability of the obtained powders was mitigated by addition of 1 ​wt% of NiO, which allowed to manufacture dense sinters at 1400 ​°C. Electrochemical impedance spectroscopy measurements done in dry synthetic air show decrease of the ionic (oxygen) conductivity with the increase of In content, as well as associated increase of the activation energy. This indicates that formed oxygen vacancies are trapped in the structure. Overall, electrical conductivity for SrCe1-xInxO3-a in H2O- and D2O-containing atmospheres decreases with In content, but respective H+ and D+ transference numbers are larger for samples with higher indium doping. At 500 ​°C the highest proton and deuterium conductivity was recorded for SrCe0.9In0.1O3-a, reaching up to 0.70·10−4 ​S ​cm−1 and 0.26·10−4 ​S ​cm−1, respectively. Derived diffusion and surface exchange coefficients are 10−7-10−6 ​cm2 ​s−1 and 10−6-10−5 ​cm ​s−1, respectively in 500–700 ​°C temperature range.

Nickel - p-block metal mixed chalcogenides based on AuCu3-type fragments: iodine-assisted synthesis as a way of obtaining new structures.

Two new mixed nickel-gallium chalcogenides, Ni9.39Ga2S2 and Ni5.80GaTe2, and a new mixed nickel-indium telluride, Ni5.78InTe2, have been synthesized by a high-temperature ampoule route with the addition of iodine, and characterized from single-crystal or powder diffraction data. They belong to the relatively uncommon Ni7-xMQ2/Ni10-xM2Q2 type of structures (M = Ge, Sn, Sb, In), and are built from p-block metal-centered nickel cuboctahedra, alternating along the c axis with defective Cu2Sb-type nickel-chalcogen ones. Both tellurium-containing compounds show a small degree of orthorhombic distortion with respect to the idealized tetragonal structure, only detectable in the powder diffraction data. No phase transition to the tetragonal structure was detected for Ni5.80GaTe2 by the in situ powder diffraction measurements from room temperature to 550 °C. DFT calculations show close relationships of electronic structures of these ternary compounds to their parent intermetallics, Ni3M (M = Ga, In). Metallic conductivity and paramagnetic properties are predicted for all three with the latter confirmed by magnetic measurements. The bonding patterns, investigated via the ELF topological analysis, show multi-centered nickel - p-block metal bonds in the AuCu3-type fragments and pairwise covalent interactions in the nickel-chalcogen fragments. Both Ni7-xMTe2 compounds showed no structural or compositional changes upon high-temperature mid-pressure hydrogenation.

Charge ordering at low temperature in lithium manganese oxide spinel

Spinels lithium manganese oxide LiMn2O4-δ synthesized from mixtures of different raw materials were used to study the relationship between the synthesis method and properties of the spinel. The investigation was emphasized on phase transition in lithium manganese oxide spinel compound at low temperature studied by means of neutron powder diffraction. It is found that the cubic structure of LiMn2O4-δ , synthesized from Li2CO3, with space group Fd-3m at room temperature was distorted to orthorhombic symmetry with space group Fddd at 290K and become more obvious down to 10K, where the splitting indicates the structural transition close to tetragonal. The equal proportion of coexisted Mn3+ (Jahn-Teller) and Mn4+ ions is associated with partial charge ordering. It is also found that the sample synthesized from LiOH.H2O and MnO x does not show phase transition at low temperatures. The extent of orthorhombic distortion is related to oxygen vacancy, δ, which is affected by the synthesis method such as the choice of starting materials, mixing method and annealing temperature.

Pressure effect on the electrical resistance of Y0.77Pr0.23Ba2Cu3O7-δ single crystals

The effect of hydrostatic pressure up to 12 kbar on the electrical resistance in the basal ab-plane of optimally oxygen-doped (δ<0.1) single crystals Y1–xPrxBa2Cu3O7–δ moderately doped with praseodymium (x≈0.23) with a critical temperature Tc≈67 K. Compared to undoped single-crystal YBa2Cu3O7–δ, doping with praseodymium led to a decrease in the critical temperature by ≈24 K with a simultaneous increase in ρab (300 K) by ≈130 μΩcm. In the region of the transition to the superconducting state, several clearly pronounced peaks are observed on the dρ/dT – T curves, which indicates the presence of several phases with different critical temperatures in the sample. The application of high hydrostatic pressure leads to an increase in Tc by about 3 K. This increase slows down with increasing pressure, and the baric derivatives, dTc/dP, decrease from 0.44 K/kbar at atmospheric pressure to 0.14 K/kbar at 11 kbar. The comparatively weak change in the critical temperature under the action of hydrostatic pressure is due to the relatively small value of the orthorhombic distortion, (a–b)/a. The change in the baric derivative dTc/dP upon all-round compression of the sample is due to the fact that, along with an increase in the Debye temperature, the matrix element of the electron-phonon interaction also increases. Possible mechanisms of the effect of high pressure on Tc are discussed taking into account the presence of features in the electronic spectrum of carriers.