Orientation controlling of Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin films prepared on silicon substrates with the thickness of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> electrodes

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates by a sol–gel route. The thickness of LSCO electrode was found to modify the preferential orientation of PZT thin films, which consequently affected the dielectric and ferroelectric properties. (100) textured PZT films with dense columnar structure could be obtained on the top of (110) textured LSCO with thickness of 230 nm. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Superconductivity on Interfaces of Nonsuperconducting Granules La<Subscript>2</Subscript>CuO<Subscript>4</Subscript> and La<Subscript>1.56</Subscript>Sr<Subscript>0.44</Subscript>CuO<Subscript>4</Subscript>

Composite materials fabricated by annealing of nonsuperconducting ceramics La₂CuO₄ and La_1.56Sr_0.44CuO₄ at 910 °C during various time are investigated. Areas of superconducting La_1.85Sr_0.15CuO₄ phase arises at boundaries of contacting nonsuperconducting granules. The volume fraction of the superconducting phase increases with increasing annealing time. A model describing the magnetic and transport properties of the samples at low magnetic fields is constructed. The magnetotransport characteristics of obtained samples at low magnetic fields (～ 100 Oe) are defined by weak links network formed by superconducting areas. At high fields, behavior of the system is defined by a magnetization of the disconnected superconducting islands. The average size of the superconducting areas has been estimated from an extended critical state model.     

Superconductivity in Ca<Subscript>0.5</Subscript>La<Subscript>0.5</Subscript>FBiSe<Subscript>2</Subscript>

Through the measurement of resistivity, magnetic susceptibility, and Hall effect, we discovered a novel BiSe₂-based superconductor Ca_0.5La_0.5FBiSe₂ with T _c of 3.9 K. A strong diamagnetic signal below T _c in susceptibility χ(T) is observed indicating the bulk superconductivity. The negative Hall coefficient throughout the whole temperature regime implies the dominant electron-type carriers in the sample. Different to most of BiS₂-based compounds where superconductivity develops from a semiconducting-like normal state, its resistivity in the present compound exhibits a metallic behavior down to T _c . Together with the enhanced T _c , the metallic character of the normal state implies that the electronic structure of Ca_0.5La_0.5FBiSe₂ may be different to those in the other BiS₂-based compounds.     

Critical Behavior Near the Paramagnetic to Ferromagnetic Phase Transition Temperature in Sr<Subscript>1.5</Subscript>Nd<Subscript>0.5</Subscript>MnO<Subscript>4</Subscript> Compound

The magnetic properties and the critical behavior in Sr_1.5Nd_0.5MnO₄ have been investigated by magnetization measurements. The magnetic data indicate that the compound exhibits a second-order phase transition. The estimated critical exponents derived from the magnetic data using various techniques such as modified Arrott plot, Kouvel–Fisher method, and critical magnetization isotherms M (T _C, H). The critical exponent values for this compound was found to match well with those predicted for the mean-field model (δ = 2.212 ± 0.124, γ = 0.975 ± 0.018, and β = 0.502 ± 0.012) at T _C = 228.59 ± 0.17. The critical exponent γ is slightly inferior than predicted from the mean-field model. Such a difference may be due, within the context of the quenched disorder and essentially the presence of the Griffiths phase. The temperature variation in the effective exponent (γ _eff) is similar to those for disordered ferromagnets.     

Structure and charge transport mechanism in hydrothermally synthesized (La<Subscript>0.5</Subscript>Ba<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript>) cubic perovskite manganite

Perovskite manganites with chemical formula La_0.5Ba_0.5MnO₃ (LBMO) samples were synthesized though the hydrothermal process by heating suitable reactants at 270?°C in an autoclave for 25 h. After washing with de-ionized water several times, the as prepared samples were then calcined at different temperatures, ranging from 120 to 1000?°C to remove the impurities. Final sintering of the sample was carried out at 1350?°C for 24 h. Subsequent X-ray diffraction (XRD) measurements were also carried out. Rietveld refinement of XRD data for the sample sintered at 1350?°C confirmed single phase cubic structure with lattice parameter a?=?3.9057? and space group P m ?3 m. The dc electrical measurements were performed in a broad range of temperatures from 77 to 870 K on this sample. The focal point of this study was to obtain microscopic parameters and characteristic length in order to discuss the relationship between magnetic, electric and phonon excitations. The electrical resistivity measurements revealed a metallic/ferromagnetic to semiconductor/paramagnetic phase transition (T_C) at 339 K. In the metallic region the experimental data best fitted the resistivity equation \(\uprho (\text{T})={\uprho _{o}}+{\uprho _2}{\text{T}^2}+{\uprho _{2.5}}{\text{T}^{2.5}}+{\uprho _{4.5}}{\text{T}^{4.5}}\) showing that the resistivity effect arises due to residual impurities, grain boundaries, electron–electron (e–e), electron–magnon (e–mag) and electron–phonon (e–ph) scattering. The analysis of the resistivity data above T_C has shown a transformation in conduction mechanism from Mott’s variable range hopping (MVRH) to small polaron hopping (SPH), around 585 K. Hopping of carriers to larger distances with multiplying values of activation energies are analyzed through MVRH below 585 K. Above 585 K, the carriers were found to be trapped by several scattering centers through small polaron, this behavior having been interpreted in the light of SPH model.     

Structural,Conductivity, and Dielectric Properties of Co<Subscript>0.5</Subscript>Mg<Subscript>0.5</Subscript>La<Subscript>0.1</Subscript>Fe<Subscript>1.9</Subscript>O<Subscript>4</Subscript> Ferrite Nanoparticles

The ferrite-based Co_0.5Mg_0.5La_0.1Fe_1.9O₄ nanoparticle system has been synthesized by using the chemical co-precipitation technique. XRD and SEM were used for the structural and morphological characterization of the nanoparticles. The XRD analysis of the synthesized samples confirmed the formation of the single-phase cubic spinel phase without any impurity or secondary phases, and the average crystallite size and lattice parameters were found as 11.89 nm and 8.376 nm, respectively. The cation distribution obtained is found as (Mg_0.19Fe_0.81)_A(Mg_0.31Fe_1.09Co_0.5La_0.1)_BO₄ from Rietveld refinement. The dielectric properties of the sample have been investigated in the frequency range of 20 Hz to 1 MHz. The DC and AC conductivity results obtained from the experiments are explained by the Verwey and correlated barrier hopping (CBH) models, respectively. The optical band gap energy of the sample is found as 0.24 eV. The results denoted the semiconductor nature of the sample, and the sample is a good candidate for applications in high-frequency transformers used for different purposes in the electronics industry.     

Effect of A-site dopant on the piezoresistive characteristics of La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript> ceramics

This letter reports the effect of the A-site doping (2, 4, and 6 mol% Bi and Li) on the piezoresistance phenomenon in La_0.8Sr_0.2MnO₃ (LSMO) polycrystalline ceramics. The fractional change in resistivity was found to be nominal for Li-modified samples but samples modified with 4 and 6 mol% Bi₂O₃ exhibited 1.8% and 2.3% fractional change in resistivity at 19.2 MPa which is significantly higher than that for pure LSMO. The enhancement in piezoresistive phenomenon is attributed to distortion of Mn–O bond due to substitution of smaller ion on to La-site. All the samples showed a sudden increase in resistivity with applied stress in the range of 0.5–2 MPa and the behavior was found to saturate as the magnitude of applied stress increases. Magnetic measurements as a function of field and temperature were conducted to confirm the A-site substitution.     

Dielectric relaxation in double perovskite oxide,Ho<Subscript>2</Subscript>CdTiO<Subscript>6</Subscript>

A new double perovskite oxide holmium cadmium titanate, Ho₂CdTiO₆ (HCT), prepared by solid state reaction technique is investigated by impedance spectroscopy in a temperature range 50–400°C and a frequency range 75 Hz–1 MHz. The crystal structure has been determined by powder X-ray diffraction which shows monoclinic phase at room temperature. An analysis of complex permittivity with frequency was carried out assuming a distribution of relaxation times as confirmed by Cole–Cole plot. The frequency dependent electrical data are analysed in the framework of conductivity and electric modulus formalisms. The frequencies corresponding to the maxima of the imaginary electric modulus at various temperatures are found to obey an Arrhenius law with an activation energy of 0·13 eV. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures. Nyquist plots are drawn to identify an equivalent circuit and to know the bulk and interface contributions.     

Magnetotransport at the LTO-LTT Structural Transition in La<Subscript>1.48</Subscript>Nd<Subscript>0.4</Subscript>Sr<Subscript>0.12</Subscript>CuO<Subscript>4</Subscript>

Magnetoresistance (MR) was measured in a La_1.48Nd_0.4Sr_0.12CuO₄ single crystal in perpendicular magnetic fields H up to 9 T in the region of the structural transition from the low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase. The hysteretic MR exhibits discrete jumps or avalanches only when the transition is approached from the LTT phase, and only during the first field sweep. The properties of the hysteresis are found to be independent of the field driving rate. The results are consistent with the presence of magnetostructural domains coupled with the charge degrees of freedom.     

Anomalous magnetic hysteresis in La<Subscript>0.6</Subscript>Sr<Subscript>0.2</Subscript>Mn<Subscript>1.2</Subscript>O<Subscript>3−δ</Subscript> manganites with a perovskite structure

We have observed an anomalous magnetic hysteresis in polycrystalline (ceramic) and single crystal (film) samples of La_0.6Sr_0.2Mn_1.2O_3−δ manganites with a perovskite structure. The anomaly is explained by the coexistence and interaction of two magnetic phases (ferromagnetic and antiferromagnetic) in these lanthanumcontaining manganites.     

Microstructure of (Na<Subscript>0.5</Subscript>La<Subscript>0.5</Subscript>)MoO<Subscript>4</Subscript> crystals coactivated with cerium and erbium ions

Crystals with the scheelite structure have been grown by the Czochralski technique from a melt of composition (Na_0.5La_0.345Ce_0.15Er_0.005)MoO₄ (NLM:Ce,Er) and have been characterized by scanning and transmission electron microscopy and x-ray microanalysis. The crystals are shown to contain carbon inclusions and CeO₂ precipitates, the latter oriented relative to the host matrix: [100]{0\(\bar 1\)2} NLM:Ce,Er ‖ [100]{0\(\bar 1\)1} CeO₂. High-temperature annealing leads to recrystallization and growth of the CeO₂ particles, which seems to be responsible for the adverse effect of annealing on the optical quality of the crystals.     

Dielectric and piezoelectric properties of YMnO<Subscript>3</Subscript> modified Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> lead-free piezoelectric ceramics

Perovskite lead-free piezoelectric ceramics Bi_0.5Na_0.5TiO₃, modified with yttrium and manganese to form a new compound, (1 − x) Bi_0.5Na_0.5TiO₃–xYMnO₃ (BNT-YM100x) with x = 0–1.2 mol%, was synthesized by a conventional solid-state reaction method. The effect of YMnO₃ on crystal structure, dielectric and piezoelectric properties was investigated. X-ray diffraction analysis shows that the materials have a single phase perovskite structure with rhombohedral symmetry. Addition of small amount of YMnO₃ improves piezoelectric properties and the optimal piezoelectric properties of d ₃₃ = 115 pC/N, k _p = 0.207 and Q _m = 260 were obtained at 0.9% YMnO₃ addition. The loss tangent tanδ is approximately constant while Curie temperature decreases with increasing YMnO₃ concentration.     

Simple explanation for the reentrant magnetic phase transition in Pr<Subscript>0.5</Subscript>Sr<Subscript>0.41</Subscript>Ca<Subscript>0.09</Subscript>MnO<Subscript>3</Subscript> perovskite

The reentrant magnetic phase transition in Pr _0.5Sr_0.41Ca_0.09MnO₃ perovskite is explained using the Ising spin model on the square lattice with mixed ferromagnetic and antiferromagnetic exchange interactions. It is shown using numerical calculations that this effect is strongly affected by the external magnetic field and lattice disorder.     

Dielectric Properties of Na<Subscript>0.7</Subscript>CoO<Subscript>2</Subscript> and of the Superconducting Na<Subscript>0.3</Subscript>CoO<Subscript>2</Subscript>·1.3H<Subscript>2</Subscript>O

We present dielectric properties of ceramic anhydrous Na_0.7CoO₂ and the superconducting Na_0.3CoO₂·1.3H₂O materials. The presence of water which induces superconductivity also may increase the dielectric constant (ε) of the hydrated material. This is consistent with the predicted relationship between the highε and the enhancement ofT _c in highT _c superconductors. The anhydrous sample is porous and the transport is due to some percolation via the pores. The porosity is much higher for the hydrated material and the transport is ionic inside bulk water.     

Anomalous magnetic susceptibility in Nd<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> manganite single crystals

Chaotic oscillations of the low-frequency magnetic susceptibility χ in a Nd_0.5Sr_0.5MnO₃ (NSMO) manganite single crystal have been observed in the temperature interval of the coexistence of the ferro- and antiferromagnetic phases of the given composition. It is established that the amplitude of χ oscillations depends on the constant bias magnetic field. The appearance of susceptibility oscillations in NSMO single crystals is attributed to the formation of magnetic transition regions, which can exist at the boundaries between ferro- and antiferromagnetic phases.     

Formation kinetics of Sr<Subscript>2</Subscript>FeMoO<Subscript>6</Subscript> double perovskite

The formation kinetics of Sr₂FeMoO₆ (SFMO) was diagnosed during the solid-state reaction of SrFeO_{3 - x} and SrMoO₄ at different temperatures and heating rates. The reaction kinetics was analyzed by X-ray diffractometer, and the extent of the reaction was quantified by the internal standard method. The non-isothermal kinetic empirical model was proposed to evaluate the activation energy and rate constant of SFMO and further justified to be valid to picture the reaction kinetics of SFMO.     

Magnetic cluster state in anion-deficient La<Subscript>0.70</Subscript>Sr<Subscript>0.30</Subscript>MnO<Subscript>2.85</Subscript> manganite

It is established that the magnetic state of the anion-deficient La_0.70Sr_0.30MnO_2.85 manganite represents the spin-glass state of the cluster. The magnetic field at the beginning (H < 10 kOe) leads to the fragmentation of ferromagnetic clusters, then (H > 10 kOe) leads to the transition to a ferromagnetic state of an antiferromagnetic matrix and to increase in the degree of polarization of local spins of manganese. It is determined that the freezing temperature of magnetic moments varies as T _f = 65 − 6H ^0.21. The causes and mechanism of the magnetic phase separation are discussed.     

Magnetic,magnetocaloric properties,and critical behavior in a layered perovskite La<Subscript>1.4</Subscript>(Sr<Subscript>0.95</Subscript>Ca<Subscript>0.05</Subscript>)<Subscript>1.6</Subscript>Mn<Subscript>2</Subscript>O<Subscript>7</Subscript>

We report the results of magnetic, magnetocaloric properties, and critical behavior investigation of the double-layered perovskite manganite La_1.4(Sr_0.95Ca_0.05)_1.6Mn₂O₇. The compounds exhibits a paramagnetic (PM) to ferromagnetic (FM) transition at the Curie temperature T _C = 248 K, a Neel transition at T _N = 180 K, and a spin glass behavior below 150 K. To probe the magnetic interactions responsible for the magnetic transitions, we performed a critical exponent analysis in the vicinity of the FM–PM transition range. Magnetic entropy change (??S _M) was estimated from isothermal magnetization data. The critical exponents β and γ, determined by analyzing the Arrott plots, are found to be T _C = 248 K, β = 0.594, γ = 1.048, and δ = 2.764. These values for the critical exponents are close to the mean-field values. In order to estimate the spontaneous magnetization M _S(T) at a given temperature, we use a process based on the analysis, in the mean-field theory, of the magnetic entropy change (??S _M) versus the magnetization data. An excellent agreement is found between the spontaneous magnetization determined from the entropy change [(??S _M) vs. M ²] and the classical extrapolation from the Arrott curves (µ₀H/M vs. M ²), thus confirming that the magnetic entropy is a valid approach to estimate the spontaneous magnetization in this system and in other compounds as well.     

Substrate effect on the properties of La<Subscript>0.775</Subscript>Sr<Subscript>0.225</Subscript>MnO<Subscript>3</Subscript> films

La_0.775Sr_0.225MnO₃ films have been produced by screen printing on various substrates (Al₂O₃, BaTi_0.85Zr_0.11Sn_0.04O₃, Ba_0.996Y_0.004TiO₃, Ba_0.996Y_0.004TiO₃ + 0.04%Mn, and Ba_0.996Y_0.004Ti_0.65Sn_0.35O₃), and their electrical properties have been studied in comparison with those of bulk materials. The structural properties of the substrates are shown to influence the electrical properties of the films.