Narrow Results

La_2/3Ca_1/3MnO₃ (LCMO) thin films with the thickness from 4 nm to 50 nm were fabricated by the off-axis magnetron sputtering technique. Single crystal (001) SrTiO₃ (STO), (0001) sapphire (ALO), and (001) yttrium-stabilized ZrO₂ (YSZ) were used as substrates. The surface morphology of thin films was characterized by atomic force microscope (AFM). The surface morphology of the thin films depends on the thickness. Thin films on STO substrates with the thickness less than 20 nm show a wave-like morphology, which indicates a two-dimension growth mode. With the thickness increases, some cracks and grains appear on the surface, which indicates the release of the lattice strain due to the lattice mismatch between the substrate and the films. The morphology became smoother with the thickness more than 30 nm, which indicates the full relaxation in strain for the film. The surface roughness and the average grain size increase with the thickness. The morphology for LCMO grows on ALO and YSZ show a rougher surface than that on STO. The rough surface morphology may indicate the wide metallic-to-insulating transition in transport properties.

In this paper, potassium sodium niobate (KNN) nanopowders were successfully obtained by sol–gel combustion method. According to thermogravimetric analysis (TGA) results, the produced xerogel was calcined at 500${}^{\circ }$C, 600${}^{\circ }$C, and 700${}^{\circ }$C to obtain KNN powders. The structural and optical properties of the prepared powders were studied using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and UV–vis spectroscopy. The XRD patterns indicated formation of orthorhombic KNN samples. The Scherrer formula and size–strain plot (SSP) method were employed to calculate crystallite size and lattice strain of the KNN powders. The TEM image revealed that the average particle size of the prepared samples is about 30 nm and they have cubic shape. The optical band gap energy of the samples was calculated using UV–vis absorbance spectra of the samples along with Tauc relation.

In this paper, we investigated the influence of rare earth ($\mathrm{\text{RE}}=\mathrm{\text{La}}$ and Gd) doped Ba${}_{0.9575}$RE${}_{0.04}$Ca${}_{0.0025}$Ti${}_{0.80685}$ Mn${}_{0.002475}$Nb${}_{0.002475}$Zr${}_{0.1782}$O₃ (BCTMNZ) ceramics were fabricated by using a conventional solid-state reaction method. The doping effects of La and Gd on the structural and magnetic properties were studied. The structural pattern of the ceramic samples were investigated by X-ray diffraction and the results indicated that both samples shows an orthorhombic structure with pure phase. Strain and crystalline size values for Gd and La doped were 0.31–0.33% and $0.154$–$0.181\mu$m, respectively. The room temperature hysteresis loops were obtained by using a vibrating sample magnetometer. La doped ceramic showed the higher value of magnetization i.e., $0.369\mu$B/f.u. as compared to Gd doped BLTMNZ ceramics.

In this paper, effects of lattice strain on dielectric properties of Sr${}_{1-x}$Ca_xBi₂Nb₂O₉ ($x=0.0$–0.5 in steps of 0.1) ceramics are reported. High frequency dipolar polarization is observed to increase for 10% calcium addition and suppresses thereafter on higher calcium concentrations. The dielectric loss values for all doped samples were lower compared to undoped one at frequencies beyond 1kHz. The sample with $x=0.1$ shows room temperature dielectric constant in the range (130$\pm$12) over a wide frequency range from 50Hz to 1MHz also minimum dielectric loss among all other sample for the same frequency range. Remarkable increase in Curie temperature ($T_c$) by 50${}^{\circ }$C is recorded in the present work by increasing 10% calcium content in SBN compostion. All higher doped samples indicate increase in $T_c$ by further higher amount. In addition, dc conductivity of all samples is measured for all samples and increase in calcium content is observed to generate more insulating compositions compared to undoped SBN with higher intrinsic activation energies.

In this study, the effect of Mn on α to γ transformation in the nanostructured high nitrogen Fe-18Cr-xMn stainless steel produced by mechanical alloying (MA) was investigated. MA was performed under nitrogen atmosphere using a high-energy planetary ball mill. X- ray diffraction (XRD) patterns of produced samples showed that α to γ transformation starts after 20 hours of milling and propagates by increasing the milling time. Completion of this phase transformation occurred in the Fe-18Cr-8Mn sample after 100 hours of milling. But, in the Fe-18Cr-7Mn sample, some α phase remained even after 150 hours of milling. Also, nitrogen analysis revealed that nitrogen solubility in the milled powders increased significantly by increasing the milling time, and ultimately reached 1wt%. This is believed to be due to the increase of the lattice defects and development of nanostructure through MA. Variations in grain size and internal lattice strain versus milling time in both cases showed that the critical ferrite grain size for austenite nucleation was lower than 10nm. Moreover, a lower transformation rate was found in samples containing lower Mn content.

A novel lead zinc titanate tungsten oxide (PbZn${}_{1∕3}$Ti${}_{1∕3}$W${}_{1∕3}$O${}_3)$ single perovskite was synthesized employing a cost-effective solid-state reaction technique. A phase transition occurs from tetragonal (P4mm) to monoclinic (C2/m) after substituting zinc (Zn) and tungsten (W) into the B-site of the pure lead titanate. The average crystallite size and micro-lattice strain are 66.2nm and 0.159%, respectively, calculated by the Williamson–Hall method. The grains are uniformly distributed through well-defined grain boundaries and the average grain size is about 17.8$\mu$m analyzed from the SEM micrograph. Raman spectrum suggests the presence of all constituent elements in the sample. The UV–Visible study suggests that the sample is suitable for photovoltaic applications because of high bandgap energy $E_g=4.17$eV. The dielectric study confirms the negative temperature coefficient resistance (NTCR) behavior of the sample. The activation energy increases from 13.9meV to 142meV with a rise of temperature suggesting that ac conductivity is thermally activated. The thermally activated relaxation process was managed by immobile charge carriers at low temperatures while defects and oxygen vacancies at higher temperatures. The presence of the asymmetrical curves in modulus plots confirms the non-Debye-type behavior. Both Nyquist and Cole–Cole semi-circular arcs confirm the semiconductor nature of the sample.

In this paper, the synthesis (solid-state reaction) and characterization (structural, dielectric, electrical, and optical) of the (BiFeO₃)${}_{0.5}$–(CaTiO₃)${}_{0.5}$ (BFCTO) are reported. The structural analysis suggests a distorted rhombohedral crystal symmetry (#R-3m) with average crystallite of 93.2nm and lattice strain of 0.105%. The scanning electron microscopy (SEM) and energy dispersive microstructural analysis X-ray (EDAX) analyses suggest that the grains are uniformly distributed with well-defined grain boundaries and the presence of all constituent elements, respectively. The average grain size is about $(4.1\pm 0.3)\mu$m as calculated from the ImageJ software. Both the temperature and the frequency-dependent dielectric study predict high dielectric constant of 9000 at 1kHz, low dielectric loss, the phase transition from ferroelectric to paraelectric at 410^∘C, and negative temperature coefficient of resistance (NTCR) character. The impedance spectroscopy provides the effect of grains and grain boundaries on the conductivity mechanism and exhibits the non-Debye type of relaxation. The decreasing radius of semicircular arcs with temperature in both Nyquist and Cole–Cole plots supports the NTCR and thermally activated conduction mechanism. The polarization–electric field (P–E) loop study confirms the ferroelectric character of the sample. The study of the $I$–$V$ plot suggests the leakage current in the mA range and ohmic conducting nature. The Fourier transform infrared spectroscopy (FTIR) spectrum suggests the presence of all constituent elements, whereas the bandgap energy from UV–Visible study is about 1.43eV, which is useful in photovoltaic applications.

In this paper, the synthesis and characterization (structural, dielectric, electrical and optical) of a double perovskite, BaSrZrMnO₆ (BSZMO), by a conventional solid-state reaction route are reported. The sample has an orthorhombic crystal symmetry with an average crystallite size of 40.7nm and a micro-lattice strain of 0.226%. A microstructural and compositional analysis was presented by using a scanning electron microscope (SEM) and energy dispersive x-ray analysis (EDX), respectively. Grains are well-grown and distributed uniformly through well-defined grain boundaries on the sample surface to enhance physical properties. EDX analysis confirms the presence of all constituent elements and is well-supported by the Raman study. The analysis of the UV–Visible spectrum reveals an energy bandgap of 2.1eV, suitable for photovoltaic applications. The study of dielectric properties as a function of temperature and frequency reveals a Maxwell–Wagner type of dispersion and explores possible applications in energy storage devices. The discussion on the impedance spectroscopy supports the negative temperature coefficient of resistance (NTCR) character whereas the modulus study suggests a non-Debye type of relaxation in the sample. The study of AC conductivity confirms a thermally activated relaxation process. Both Nyquist and Cole–Cole plots support the semiconducting nature of the sample. The study of resistance versus temperature ($R\sim T$) supports NTC thermistor character for temperature sensor applications. The analysis of the P-E loop reveals the possibility of the ferroelectrics’ character.

In the present investigation, the synthesis of the strontium copper titanate $({\mathrm{\text{Sr}}}_3{\mathrm{\text{CuTi}}}_4{\mathrm{\text{O}}}_{12},\mathrm{\text{SCTO}})$ ceramic by the cost-effective solid-state reaction was reported. The structural analysis suggests a single-phase tetragonal crystal symmetry with space group P4/mmm. The average crystallite size and mechanical compressive microlattice strain are found to be 65.8nm and 0.000594, respectively. The study of the field emission scanning electron microscope (FESEM) micrograph suggests that grains and grain boundaries are uniformly distributed on the sample surface with less porosity. The study of Raman lines suggests the presence of all constituent elements, which is well supported by EDAX analysis. The UV–Vis spectroscopy analysis shows that the bandgap of SCTO is about 3.2eV suitable for photovoltaic and other higher-temperature sensor applications. The decrease of dielectric constant with frequency supports the reduction of space charge polarization. The modulus analysis suggests that the immobile charge carriers at lower and defects and oxygen vacancies at higher temperatures are responsible for the thermally activated conduction process. The calculated activation energies are 4.54meV, 4.40meV, 3.39meV and 3.29meV at 1kHz, 10kHz, 100kHz and 1MHz; the decrease with the rise of the frequency confirms a thermally activated conduction process. Thermistor constant $(\beta )$, sensitivity factor $(\alpha )$ and stability factor of the sample were calculated, which confirms the characteristics of the NTC thermistor. The Nyquist and Cole–Cole semicircular arcs confirm NTCR character and are found to be suitable applications for energy storage devices and thermistors.