Phase Transition In La0 Research Articles

Dynamics of crystallization and phase transition in La0.5Sr0.5CoO3 thin films

Dynamics of crystallization and phase transitions were investigated in La0.5Sr0.5CoO3 films with four-probe resistance electrical measurements and x-ray diffraction. Nucleation of crystalline phases from the amorphous phase of La0.5Sr0.5CoO3 was found to start at a temperature of 325 °C. It is very interesting to note that the crystallization completes within a very narrow temperature range of 390–420 °C, and recrystallization occurs at 560 °C. In addition, electron–phonon, electron–grain boundary, and electron–defect interactions, as well as oxygen contents were found to be important factors in various temperature regions during the resistance measurement. The metallic phase La0.5Sr0.5CoO3 films can only be obtained if the films were directly heated to higher than 750 °C. The sequence and knowledge of phase transitions observed for La0.5Sr0.5CoO3 are expected to be ubiquitous for perovskite oxide compounds in general.

Low Frequency Internal Friction Study of Phase Transition in La0.95K0.05MnO3 Bulk Materials

La 0.95 K 0.05 MnO 3 has been studied with reference to the internal friction, electrical resistance and ac magnetic susceptibility. Large magnetoresistance (MR) exists in a wide temperature range (20-275 K) in La 0.95 K 0.05 MnO 3 specimens at a small magnetic field (0.3 T). The resistance has a sharp peak at about 265 K, and the MR has a sharp peak at about 259 K. The internal friction measurement reveals a peak at about 268 K, accompanied with a minimum of elastic modulus. The position of the peak in Q -1 does not shift with frequency, but the height of the peak in Q -1 decreases with increasing frequency, which is a general character of the low frequency internal friction associated with the phase transition. The apparent activation energy of the phase transition E ap was obtained as 0.53 eV.

Low Frequency Internal Friction Study of Phase Transition in La0.95K0.05MnO3 Bulk Materials

La-{0.95}K-{0.05}MnO-3 has been studied by the internal friction, electrical resistance and AC magnetic susceptibility. Large magnetoresistance (MR) exists in a wide temperature range (20～275K) in La-{0.95}K-{0.05}MnO-3 specimen at low magnetic field (0.3T). A sharp peak (T=267K) and a shoulder peak (T=220K) are observed in the R-T curve. Accompanied with the local minimum of elastic modulus, the internal friction measurement reveals two peaks at about 268K and 230K. The position of the peaks in Q+{-1} do not shift with frequency, but their height of the peaks in Q+{-1} decrease with frequency increasing, which are general characters of the low frequency internal friction associated with the phase transition. The apparent activation energy of the phase transition E-{ap} was obtained as 0.53eV. From above experiments we draw the conclusion that there exists the phase separation in the sample.

Electron spin resonance and longitudinal relaxation around phase transition in La0.9Ca0.1 MnO3

With original modulation technique, the longitudinal electron spin-relaxation timeT 1 has been measured in the La1-xCaxMnO3 manganite (x = 0.1) both in the paramagnetic state and around the temperature (T c) of the ferromagnetic ordering. The data are compared with the evolution of the transverse relaxation time T2 as determined from the electron spin resonance (ESR) linewidth. Well above Tc, theT 1 =T 2 equality was confirmed, whereas a steep slowing down ofT 2 was observed asT c was approached (theT 1/T2 ratio increased by two orders of magnitude). The temperature dependence ofT 1 within the whole temperature range was found to be consistent with that ofT · χ(T), where χ(T) is the electron-spin susceptibility obtained from the ESR absorption area. The interpretation suggests that both the longitudinal and transverse electron-spin relaxation rates are governed by strong exchange interaction between the Mn ions, the ESR linewidth being inhomogeneously broadened in the vicinity of the phase transition.

Features of high-frequency ultrasound propagation in the temperature range of structural and magnetic phase transitions in La1−x SrxMnO3 (x=0.175) manganite

The propagation of ultrasonic waves at a frequency of 770 MHz in a La0.825Sr0.175MnO3 single crystal is investigated in the temperature range 350–150 K. It is found that the velocity, attenuation, and mode composition of ultrasonic waves change at temperatures of 315–280 and 220 K. These changes correlate with the structural and magnetic phase transitions and can be explained in terms of the Jahn-Teller distortions of the crystal lattice.

Phase transitions in La1−x CaxMnO3−x/2 manganites

The crystal structure parameters and magnetic and electrical properties of La1−x CaxMnO3−x/2 reduced manganites with 0≤x≤0.5 are established. These investigations contribute to the understanding of magnetic interactions in manganites without Mn4+ ions. It is found that these manganites show a long-range antiferromagnetic order up to x=0.09 and transform into spin glasses at 0.09<x≤0.35. The compositions in the range 0.35<x≤0.5 show a strong increase in the spontaneous magnetization and critical point associated with the appearance of spontaneous magnetization and can therefore be viewed as inhomogenious ferromagnets. The magnetic and crystal structure peculiarities of La0.5Ca0.5MnO2.75 are established by the neutron diffraction method. The strongly reduced samples show a large magnetoresistance below the point where the spontaneous magnetization develops. The magnetic phase diagram of La1−x CaxMnO3−x/2 is established by magnetization measurements. The magnetic behavior is interpreted assuming that the Mn3+-O-Mn3+ magnetic interaction is anisotropic (positive-negative) in the orbitally ordered phase and isotropic (positive) in the orbitally disordered phase. Introduction of the oxygen vacancies changes the magnetic interaction sign from positive to negative, thereby leading to a spin glass state in strongly reduced compounds. The results obtained reveal unusual features of strongly reduced manganites such as a large ferromagnetic component, a high magnetic ordering temperature, and a large magnetoresistance despite the absence of Mn3+-Mn4+ pairs. In order to explain these results, the oxygen vacancies are supposed to be ordered.

Features of the rhombohedral-to-orthorhombic structural phase transition inLa1−xSrxMnO3

Features of the rhombohedral-to-orthorhombic structural phase transition in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">La</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi>−</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MnO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Thermal-expansion and magnetostriction anomalies in phase transitions in La1−x SrxMnO3

A study is reported on phase transitions in the La1−x SrxMnO3 system, both spontaneous and induced by a pulsed magnetic field of up to 250 kOe, accompanied by anomalies in magnetoelastic properties. The temperatures of the polaron (charge) and magnetic ordering, as well as those of structural transitions, are observed to be in good agreement with the results obtained by other methods. Jumps in the field dependence of longitudinal and transverse magnetostriction associated with field-induced orbital ordering have been found. A strong temperature dependence of the corresponding threshold fields is observed.

Elastic-moduli and ultrasonic-attenuation anomalies near antiferromagnetic phase transitions in La1−xCaxMnO3

Both the longitudinal and transverse ultrasonic sound velocities and attenuations in the single-phase polycrystalline compound La1−xCaxMnO3 (x=0.63,0.83) have been measured by a conventional pulse-echo-overlap technique at a frequency of 10 MHz, between 50 and 300 K. The variations with temperature of the Young modulus E, shear modulus G, bulk modulus B, Poisson’s ratio σ, and attenuation α have been determined. Anomalies in E, G, B, σ, and α were observed near the temperature of the charge-ordering transition TCO and antiferromagnetic (AFM) transition TN. The results imply a very strong spin–phonon interaction caused by linear magnetostriction near the AFM transition. The detailed form of the anomalies is different for different types of phase transitions.

Structural and magnetic phase transitions in La0.9Sr0.1MnO3

A study is made of phase transitions in doped La0.9Sr0.1MnO3 compounds using combined x-ray, electrical, and magnetic measurements. Structural phase transitions are observed accompanied by a change in the cell volume at temperatures of 100–110 K and 300–340 K. These structural changes are found to be related to different contributions of the rhombic Jahn-Teller Q 2 mode to the formation of the crystal lattice. The structural transition at 100–110 K is accompanied by distinctive magnetic and electrical properties. The data are analyzed in detail.

New aspect of low-temperature phase transitions of La-cuprates

The change in the microstructure on aging at 12 K below a low-temperature structural phase transition in La1.5Sr0.1Nd0.4CuO4 has been examined by transmission electron microscopy. From a seriesof 100 forbidden dark field images obtained inin situ observation, spotty-shape regions with a Pccn/LTT tilt of the CuO6 octahedron were found to be nucleated and grow inside a LTO domain, accompanying the annihilation of some spotty-shape regions. In addition, there exists a tweed texture in fundamental dark field images, which is due to the macroscopic strain involved in the transition. Because a mapof the tweed texture is different from that of the spotty-shape region, the tilt of the octahedron is not always coupled to a proper spontaneous strain.

Magnetostructural phase transitions in La1−xSrxMnO3with controlled carrier density

Magnetostructural phase transitions in La_1−<i>x</i>Sr_<i>x</i>MnO₃with controlled carrier density

Pressure effects on superconductivity and structural phase transition in La1.8−xNd0.2BaxCuO4

The structural transition at T1(∼110 K) of La1.8−xNd0.2BaxCuO4 (x=0.1) disappears above 1GPa, but the superconducting critical temperature Tc increases monotonically with pressure over the whole pressure range examined (0≤P≤2GPa). On the other hand, the structural transition for x=0.125 persists up to, at least, 2GPa, though it jumps to the temperature T*(∼60 K), where the charge (hole) ordering occurs, at pressures above 1.5GPa. The structural change for x=0.125 is appreciably depressed at P≥1.5GPa and Tc is largely restored.

Microtwin Domains and Phase Transitions in La1.85−x Ndx Sr0.15 CuO4

Microstructural phenomena and phase transitions of the Nd-doped La1.85 Sr0 15 CuO4 system are studied in an electron microscope. In ion-milled samples, twin domains appear and disappear as expected at the high temperature phase transition. At temperatures below the high temperature transition, these twin domains show a very subtle behaviour. Ground material even in the orthorhombic phase shows no twins at all. In ion-thinned material a typical reduction of the domain size occurs after an electron illumination time of about one hour. Generally no reversible change of the twin configuration could be observed at the low temperature phase transition. Mikrostruktur and Phasenübergänge von Nd-dotiertem La1.85 Sr0.15 CuO4 werden im Elektro-nenmikroskop untersucht. Wie erwartet, erscheinen und verschwinden Zwillingsbereiche am Hoch-temperaturphasenübergang in ionengedünnten Proben. Unterhalb dieses Phasenüberganges zeigen die Zwillingsbereiche ein sehr subtiles Verhalten. Gemörsertes Material zeigt selbst in der orthorhombischen Phase keine Zwillingsbildung. In ionengedünntem Material tritt eine typische Reduzierung der Bereichsgröße nach einer Bestrahlungszeit von etwa 1 h ein. Generell kann am Tieftempartur-Phasenübergang keine reversible Änderung der Zwillingskonfiguration beobachtet werden.

A Low-Temperature X-Ray Diffraction Study of Structural Phase Transition in La1.86Sr0.14CuO4

Using high-quality single crystal samples, the structural phase transition in La1.86Sr0.14CuO4 was investigated by the low-temperature X-ray diffraction method in the range from ambient temperature down to 10 K. The transition temperature from tetragonal to orthorhombic lattice was determined to be 182.5±2.5 K, and neither the monoclinic nor the new tetragonal phase was detected. Since no noticeable change was found in the peak width of (004)t during the phase transition, the shear was estimated to be confined in the direction normal to [001]t. The tilt angle between adjacent domains, determined by (220)t reflection, was of a very small value as 0.013±0.002° at 10 K. This may be related to the observed fourfold symmetry of the upper critical field (HC2) in the plane of (001)t.

Evidence of Phase Transition in La1.85CuO4+Δ by Thermal Conductivity

physica status solidi (a)Volume 119, Issue 1 p. K53-K57 Short Note Evidence of Phase Transition in La1.85CuO4+Δ by Thermal Conductivity J. Mucha, J. Mucha Institute for Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław Search for more papers by this authorA. Jeżwski, A. Jeżwski Institute for Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław Search for more papers by this author J. Mucha, J. Mucha Institute for Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław Search for more papers by this authorA. Jeżwski, A. Jeżwski Institute for Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław Search for more papers by this author First published: 16 May 1990 https://doi.org/10.1002/pssa.2211190151Citations: 1 Okólna 2, PL-50-422 Wrocław, Poland. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume119, Issue116 May 1990Pages K53-K57 RelatedInformation