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We report on the first observation of the macroscopic (long-range) Si[Single_Bond]SiO2 phase separation in Si-rich oxide SiOx (x<2) obtained by continuous-wave laser annealing of free-standing SiOx films. The effect is analyzed by a unique combination of microscopic methods (Raman, transmission, photoluminescence, and infrared spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy). Three regions can be distinguished on a SiOx free-standing film after 488 nm laser annealing at intensities above ∼104 W cm-2: central spot, ring around the central spot, and pristine film outside the irradiated area. In the pristine SiOx material, small Si nanocrystals (Si-nc) (diameters of a few nanometer) are surrounded by SiO2 with an addition of residual suboxides, the Si-nc being produced by annealing at 1100 °C in a furnace. The central spot of the laser-annealed area (up to ∼30 μm wide in these experiments) is practically free of Si excess and mainly consists of amorphous SiO2. The ring around the central spot contains large spherical Si-nc (diameters up to ∼100 nm) embedded in amorphous SiO2 without the presence of suboxides. Laser-induced temperatures in the structurally modified regions presumably exceed the Si melting temperature. The macroscopic Si[Single_Bond]SiO2 phase separation is connected with extensive diffusion in temperature gradient leading to the Si concentration gradient. The present work demonstrates the advantages of high spatial resolution for analysis in materials research. [ABSTRACT FROM AUTHOR]

The phase separation of Nd0.5Ca0.5-ySryMnO3, for 0≤y≤0.5, is studied via electron spin resonance (ESR) in the temperature range 80–400 K. Two types of magnetic phases are found to coexist in the samples with y>0 below a phase separation temperature T*. The ESR line width exhibits a minimum near the charge order transition temperature TCO for samples with y<0.25, and near T* for y≥0.25. A systematic decrease in line width is observed as y increases from 0 to 0.5. The g factors increase slightly and the ESR intensities increase exponentially when the temperature decreases in the paramagnetic region. Our results demonstrate presence of two local magnetic structures due to the intrinsic phase separation. [ABSTRACT FROM AUTHOR]

Phase separation (PS) in hole-doped cobaltites (La1-xSrxCoxO3) is drawing renewed interest recently. In particular, the magnetic behavior of La0.85Sr0.15CoO3 has been subjected to a controversial debate for the past several years; while some groups show evidence for magnetic PS, others show spin glass (SG) behavior. Here, an attempt is made to resolve the controversy related to “PS versus SG” behavior in this compound. We present the results of a comprehensive investigation of the dc magnetization, ac susceptibility, and the magnetotransport properties of La0.85Sr0.15CoO3 samples. We contemplate that the magnetic PS in La0.85Sr0.15CoO3 is neither intrinsic nor inherent, but it is a consequence of the preparation conditions. It is realized that a low temperature annealed (LTA) sample shows PS whereas the high temperature annealed (HTA) sample shows SG behavior. The Brillouin-like behavior of field cooled dc magnetization and apparently no frequency dependent peak shift in ac susceptibility for the LTA sample characterize it to be of ferromagneticlike whereas a kink in field cooled dc magnetization and a considerable amount (∼3 K) of frequency dependent peak shift in the ac susceptibility for the HTA sample characterize it to be of SG state. The magnetotransport properties show that the HTA sample is more semiconducting as compared to the LTA sample. This is interpreted in terms of the presence of isolated as well as coalescing metallic ferromagnetic clusters in the case of LTA sample. The magnetoresistance (MR) at 10 K for the HTA sample exhibits a huge value (∼65%) as compared to the LTA sample, and it monotonically decreases with the rise in temperature. Such a high value of MR in the case of HTA sample is strongly believed to be due to the spin dependent part of random potential distribution. Further, the slow decay of remnant magnetization with progress of time and the existence of hysteresis at higher temperatures (up to 200 K) in the case of LTA sample as compared to the HTA sample clearly unveil different magnetic states associated with them. [ABSTRACT FROM AUTHOR]

We have investigated the details of phase separation in the electron-doped manganites Sm1-xCaxMnO3 (0.8≤x≤0.92) by using temperature dependent x-ray diffraction. The lattice of the low-temperature orthorhombic phase is distorted to various extents according to the strength of the coexisting monoclinic phase. Meanwhile, the room-temperature lattice becomes more distorted due to the increasing Jahn–Teller active Mn3+ ions by Sm3+ doping. On the other hand, the substitution of Ca2+ with Sm3+ introduces the Mn3+–Mn4+ pairs, which favor the double exchange ferromagnetism. As a result of the competition between the lattice distortion and electron doping level, the modified phase diagram have been presented, including the high-temperature Griffiths phase and the ground state with competing multiphases. [ABSTRACT FROM AUTHOR]

Both La0.375Pr0.25Ca0.375MnO3 (LPCMO) and La0.625Ca0.375MnO3 (LCMO) were found to exhibit coexistence of competing orders (phase separation) over a wide temperature range. However, substantial hysteretic behaviors in both of the temperature-dependent resistance [R(T)] and magnetization [M(T)] [also known as the persistent magnetic memory effect (PMME)] are only displayed in LPCMO. The results indicate that, in LPCMO, the size distribution of the coexisting charge-ordered insulating and metallic ferromagnetic (FM) phases plays a determinant role in the PMME effects in different temperature regimes. Moreover, due to the direct competition between the two coexisting phases, the system is most susceptible to the external applied field in the hysteretic temperature region. On the other hand, in LCMO, the phase transition between paramagnetic and FM is more like an isomorphic transition in pure materials, and thus does not show significant hysteresis. [ABSTRACT FROM AUTHOR]

Systematic studies of magnetic, electrical, and thermal transport properties have been performed on a single crystal of La0.98Pb0.02Mn0.74Co0.25O3. From 5 to 500 K, the material system shows three distinct magnetic states, a low-temperature glassing state (from 5 to 185 K), a Griffiths-like ferromagnetic state (from 185 to 326 K), and a single paramagnetic phase above 326 K. The sample shows a semiconducting electrical transport behavior in the whole studied temperature range. With decreasing temperature, magnetoresistance increases rapidly from 290 K and reaches a maximum at 185 K and then decreases continuously with a broad peak in the vicinity of 100 K. Magnetothermopower also presents obvious anomalies at these characteristic temperatures. Both the magnetic and transport properties suggest an intrinsic phase separation in the single crystal. [ABSTRACT FROM AUTHOR]

The magnetic, resonance, and electric properties of LaxMnO3+δ (0.815≤x≤1.0) polycrystalline samples have been studied in the temperature range of 77–370 K and at high pressures of up to 11.5 kbar. It is shown that the increase in the La/Mn ratio gives rise to a change in the low temperature magnetic state from ferromagnetic to cluster spin glass, as well as to a drastic transformation of electric properties. A peculiar double-peaked shape is characteristic of the resistivity versus temperature curves for the intermediate range of x values. Within this range, the application of high pressures drastically changes both the value of resistivity and the character of its temperature dependence. It is shown that the approach, which regards the state of LaxMnO3+δ polycrystals as a mixture of interpenetrating paramagnetic insulating and ferromagnetic metallic phases, is able to successfully describe the peculiarities of the temperature dependence of total resistivity, as well as the features of its transformation under hydrostatic compression. It is demonstrated that the formation of a low temperature resistance peak is a result of a wide-temperature-region coexistence of the phases, which exhibits opposite trends in the temperature dependences of resistivity. The conclusion is made that not only does hydrostatic compression result in drastic changes in the relative volume fractions of the coexisting phases, but it also affects the intrinsic parameters of each of the phases. [ABSTRACT FROM AUTHOR]

The capping of GaN quantum dots (QDs) with an Al0.5Ga0.5N layer is studied using transmission electron microscopy and atomic force microscopy in combination with theoretical calculations. The capping process can be divided into several well-distinguishable stages including a QD shape change and a local change of the Al0.5Ga0.5N capping layer composition. The phase separation phenomenon is investigated in relation with the capping layer thickness. Amount of the chemical composition fluctuations is determined from separate analysis of scanning transmission electron microscopy and high-resolution transmission electron microscopy images. The local distortion of atomic lattice in the QD surroundings is measured by high-resolution electron microscopy and is confronted with theoretically calculated strain distributions. Based on these data, a possible mechanism of alloy demixing in the Al0.5Ga0.5N layer is discussed. [ABSTRACT FROM AUTHOR]

Structural, magnetic, and electronic transport properties of Bi0.6-xLaxCa0.4MnO3 (0≤x≤0.6) manganites have been studied systematically. The parent compound exhibits robust charge ordered antiferrromagnetic (COAFM) phase with TCO∼293 K and AFM Néel temperature TN∼149 K. The sample with x=0.1 show a M(T) curve of 'arch bridge' form between 142 and 253 K, which is attributed to the AFM peak embedded in the broad transition of the CO. For the middle doping samples (0.2≤x≤0.4), although the CO peaks disappear as a result of the suppression of the long range CO state, AFM superexchange coupling has been strengthened with the increasing of La doping level. The Bi0.1La0.5Ca0.4MnO3 sample shows interesting phenomena such as magnetization steps and magnetic memory effect. The resistivity of the samples exhibits insulating behavior in our measured temperature range for x≤0.4. While both x=0.5 and x=0.6 compounds exhibit metal-insulator transition. Furthermore, large low field magnetoresistance (MR) and hysteresis appears only in the MR(H) curve of x=0.5 sample. These results are discussed in terms of the charge localization caused by the lattice distortion due to the character of the 6s2 lone pair of Bi3+ ions. [ABSTRACT FROM AUTHOR]

The phase separation of Nd0.5Ca0.5-ySryMnO3, for 0≤y≤0.5, is studied via electron spin resonance (ESR) in the temperature range 80–400 K. Two types of magnetic phases are found to coexist in the samples with y>0 below a phase separation temperature T*. The ESR line width exhibits a minimum near the charge order transition temperature TCO for samples with y<0.25, and near T* for y≥0.25. A systematic decrease in line width is observed as y increases from 0 to 0.5. The g factors increase slightly and the ESR intensities increase exponentially when the temperature decreases in the paramagnetic region. Our results demonstrate presence of two local magnetic structures due to the intrinsic phase separation. [ABSTRACT FROM AUTHOR]

Semiconductor nanospheres were efficiently synthesized by the pulsed-laser-ablation-in-liquid technique applied to suspensions of certain powders. The nanosphere formation is demonstrated to follow a solid phase separation mechanism and take place in a low-temperature zone of the laser-irradiated volume, while the high temperature and rapid cooling rate generated by pulsed laser are crucial for the particle shape. The synthetic route is applied to different material systems and proved to be a general way for manufacturing various high-quality nanostructures with spherical shape. [ABSTRACT FROM AUTHOR]

The macroscopic phase separation of undercooled liquid Fe50Sn50 immiscible alloy was investigated by both drop tube experiment and the modified Model H. Core-shell structures with two, three, and five layers were formed during experiment. The concentric shells comprised of Fe-rich phase and Sn-rich phase distribute periodically in the solidified droplet, and the Sn-rich phase is always located at the sample surface owing to its smaller surface tension. The simulated results of modified Model H reproduce core-shell structures with the same layers, which justifies the prediction of this model. If the fluidity parameter Cf and solute concentration [lowercase_phi_synonym] satisfy the physical conditions of both Cf<1 and 0<[lowercase_phi_synonym]<0.45 or Cf≥1, the phase separation morphology exhibits the double-layer core-shell structure, whereas the multilayer core-shell structure is expected to form under the conditions of both Cf<1 and 0.45≤[lowercase_phi_synonym]<0.5. The forming ability of core-shell structure for various immiscible alloys can be predicted accordingly. [ABSTRACT FROM AUTHOR]

Indium-rich AlInN are grown by metal-organic (MO) chemical vapor deposition using trimethylaluminum, trimethylindium, and ammonia. Under the conservation of MO influx, the effects of gas flow in the MO route on AlInN growth and Al-related parasitic reaction are investigated. With an increase in this gas flow, the suppression of Al-related parasitic reaction, i.e., enhancement in Al content incorporation and improvement of crystalline quality, is satisfactorily shown until the occurring of severe phase separation. Accordingly, Al content x in AlxIn1-xN can be tuned from x=0.02 to 0.26. The Raman spectra of those AlInN samples with phase separation are analyzed by the resonant excitation effect and two-mode behavior for A1(LO). Finally, we propose a phase diagram to interpret the phase separation and Al content evolution under the influence of gas flow. [ABSTRACT FROM AUTHOR]

Systematic studies of magnetic, electrical, and thermal transport properties have been performed on a single crystal of La0.98Pb0.02Mn0.74Co0.25O3. From 5 to 500 K, the material system shows three distinct magnetic states, a low-temperature glassing state (from 5 to 185 K), a Griffiths-like ferromagnetic state (from 185 to 326 K), and a single paramagnetic phase above 326 K. The sample shows a semiconducting electrical transport behavior in the whole studied temperature range. With decreasing temperature, magnetoresistance increases rapidly from 290 K and reaches a maximum at 185 K and then decreases continuously with a broad peak in the vicinity of 100 K. Magnetothermopower also presents obvious anomalies at these characteristic temperatures. Both the magnetic and transport properties suggest an intrinsic phase separation in the single crystal. [ABSTRACT FROM AUTHOR]

In this paper we report a study of phase separation in bulk InxGa1-xN films grown by metal organic chemical-vapor deposition using mid-UV Raman spectroscopy. Evidence of phase separation is observed by the occurrence of low frequency shoulders identified as minority phase in the A1(LO) Raman mode. A phase transition in the alloy from the metastable to unstable region was found to be occurring at an indium concentration of about 25%. Raman spectroscopic results also indicate that the compositional inhomogenity in our samples increase, as would be expected, with depth in the film. A direct correspondence is also found between the percentage of indium concentration in the film and the amount of compositional inhomogenity. [ABSTRACT FROM AUTHOR]

Structural, magnetic, and electronic transport properties of Bi0.6-xLaxCa0.4MnO3 (0≤x≤0.6) manganites have been studied systematically. The parent compound exhibits robust charge ordered antiferrromagnetic (COAFM) phase with TCO∼293 K and AFM Néel temperature TN∼149 K. The sample with x=0.1 show a M(T) curve of 'arch bridge' form between 142 and 253 K, which is attributed to the AFM peak embedded in the broad transition of the CO. For the middle doping samples (0.2≤x≤0.4), although the CO peaks disappear as a result of the suppression of the long range CO state, AFM superexchange coupling has been strengthened with the increasing of La doping level. The Bi0.1La0.5Ca0.4MnO3 sample shows interesting phenomena such as magnetization steps and magnetic memory effect. The resistivity of the samples exhibits insulating behavior in our measured temperature range for x≤0.4. While both x=0.5 and x=0.6 compounds exhibit metal-insulator transition. Furthermore, large low field magnetoresistance (MR) and hysteresis appears only in the MR(H) curve of x=0.5 sample. These results are discussed in terms of the charge localization caused by the lattice distortion due to the character of the 6s2 lone pair of Bi3+ ions. [ABSTRACT FROM AUTHOR]