Phase Transition Peak Research Articles

Growth of 0.91PZN-0.09PT Single Crystal and Effect of Poling on Their Properties

Single crystals of 0.91PZN-0.09PT were grown by flux method. (001) oriented crystal plates were poled under different electric fields. Dielectric measurements show a phase transition peak at 460 K in unpoled samples. Poled samples show an additional anomaly around 360 K. Heat flow measurements also reflect a hump near 450 K in unpoled crystals. The hump gets diffused as we increase the poling field. As we pole the sample at 6kV/cm, before carrying out the heat flow measurement, the hump disappears.

In-plane anisotropy in the microwave dielectric properties of SrTiO3 films

Microwave tunable dielectric properties of strained (001) SrTiO3 thin films epitaxially deposited on (110) DyScO3 substrates were studied for in-plane film orientations ([100], [010], [110], and [−110]). A significant in-plane anisotropy in dielectric constant and tuning was observed in these SrTiO3 films. The highest dielectric constant and tuning at room temperature are observed along the [010] direction of the SrTiO3 film (1000 Å thick) (3500 and 70% at 1V∕μm, respectively), the lowest ones are observed along the [100] direction (i.e., 2000 and 50% at 1V∕μm, respectively). The dielectric constant and tuning along [−110] and [110] are about 2500 and 30% at 1V∕μm, respectively, which are intermediary to those along the [010] and [100] directions. The dielectric Q(=1∕tanδ) does not show any large difference for the four directions (i.e., Q∼10−20). Also, the phase-transition peak for the [−110] and [110] directions of the SrTiO3 film (300 Å thick) is observed at 275 K, which is lower than that for the [010] and [100] directions. The observed in-plane anisotropic dielectric properties have been interpreted based on the phenomenological thermodynamics of film strain.

Zener relaxation peak in a Cu–Al–Mn shape memory alloy

We have studied the temperature spectra of internal friction and relative dynamic modulus of a Cu–11.9Al–2.5Mn (wt.%) alloy. It is found that a peak appears at around 350 °C during the first heating process of the quenched specimen. The peak occurs not only during heating but also during cooling. Its activation energy has been calculated to be 1.85±0.17 eV in terms of the Arrhenius relation. In addition, the peak disappears in specimens during the second or more heating process, because an overlap occurs between the peak and the reverse martensitic phase transition peak. During cooling, however, the peak can be seen all the time. It is suggested that the peak originates from Zener relaxation.

Room-temperature tunable microwave properties of strained SrTiO3 films

Structural distortion of ferroelectric thin films caused by film strain has a strong impact on the microwave dielectric properties. SrTiO3 thin films epitaxially grown on (110)DyScO3 substrates using molecular beam epitaxy are extremely strained (i.e., ∼1% in-plane tensional strain) from 3.905Å of bulk SrTiO3. The room-temperature in-plane dielectric constant and its tuning of the films at 10GHz are observed to be 6000 and 75% with an electric field of 1V∕μm, respectively. The control of strain in SrTiO3 provides a basis for room-temperature tunable microwave applications by elevating its phase-transition peak to room temperature.

Polarization response of proton irradiated 0.9Pb(Mg1∕3Nb2∕3)O3-0.1PbTiO3∕polyvinylidene fluoride-trifluoroethylene 0-3 composites

Polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE) 70∕30mol%] copolymer can be transformed from a normal ferroelectric to a relaxor ferroelectric material after proton irradiation. The phase transition peak broadens and shifts towards lower temperature as the measurement frequency decreases. The occurrence of a slim polarization-electric field loop is another evidence of the effect of proton irradiation. In the present study, 0-3 composites are fabricated by incorporating 0.9Pb(Mg1∕3Nb2∕3)O3-0.1PbTiO3 ceramic powder into a P(VDF-TrFE) 70∕30mol% copolymer matrix. 0.9PMN-0.1PT ceramic is a relaxor ferroelectric with high dielectric permittivity. It was found that the relative permittivity of an unirradiated PMN-PT∕P(VDF-TrFE) 0-3 composite increases with increasing ceramic volume fraction. With a dosage of 1000kGy (where 1Gy=100rad), the composite exhibits a broad peak in the relative permittivity. In the unirradiated composites, the remnant polarization increases gradually with PMN-PT volume fraction. After irradiation, the remnant polarization of the composites with different PMN-PT volume fractions is similar to that of the irradiated copolymer. Energy storage capabilities of the samples were evaluated which showed that proton irradiated composites have a potential for energy storage applications.

Phase transformation in BST ceramics investigated by internal friction measurements

Ferroelectric (BaSr)TiO 3 materials are widely used for numerous applications in microelectronic ranges. This paper concerns investigation of variation of internal friction and shear modulus versus temperature in a low frequency range for Ba x Sr 1− x TiO 3 systems ( x = 0.4, 0.55, 0.7 and 0.8). This makes it possible to report energy dissipation phenomena such as phase transitions and relaxation processes due to interactions between domain walls and oxygen vacancies. Temperature of loss peak for each phase transition decreases and peaks become more diffuse with increasing Sr content in BST materials. An experimental phase diagram has been established for Ba x Sr 1− x TiO 3 systems. Effects of MgO doping have been investigated for the composition x = 0.8. Both level of mechanical loss and temperatures of phase transitions are sensitive to the Mg dopant.

Internal friction in hard and soft PZT-based ceramics

This study concerns the two following commercial ceramics: PZT TRS100 (US Navy I standard: hard material) and PZT TRS600 (US Navy VI standard: soft material). These materials are PZT ceramics with various dopants. Internal friction and elastic modulus measurements have been performed versus temperature at different frequencies. Considering the hard ceramic, two relaxation peaks (R1, R2) related to oxygen vacancies–domain walls interaction were observed similarly to undoped PZT ceramics. In addition, a phase transition peak (P1) occurs at the Curie temperature. Considering the soft ceramic, only two phase transition peaks were observed. The increase of modulus associated with the phase transition internal friction peak occurs at the Curie temperature in both samples. The effects of some dopants are investigated. Some of them influence either the concentration of oxygen vacancies or the domains structure.

Transport properties of colossal magnetoresistance of Pr2/3Sr1/3MnO3 film

Measurements of the thermopower were carried out, from room temperature down to 10K, on the colossal magnetoresistance (CMR) thin films of the Pr2/3Sr1/3MnO3(PSMO) sample, which showed a dramatic reduction in the 1/f noise spectrum reported previously. At low temperatures, the thermopower is negative and shows metallic diffusion behavior of linear temperature dependence. As the temperature goes up near 150K, the thermopower reduces dramatically to show the behavior of 1/T temperature dependence,which is consistent with the prediction of the small polaron model for the high temperature phase of CMR materials. Compared with the temperature dependence of the resistance and the property of the 1/f noise near the phase transition peak, the conclusion can be reached that the percolation-typed phase separation exists in the phase transition temperature region.

Pressure dependence of thermal decomposition of ammonium nitrate oxidizer

There is an increasing interest in research and development of ecofriendly solid propellant systems which can replace the existing ones in applications particularly where the rockets have to be fired in close proximity ofthe personnel and smokeless HCI-free burning is desired. Ammonium nitrate (AN) is receiving wide attention as a possible substitute for ammonium perchlorate oxidizer in view of the hazardous nature of other candidates like nitramines and non-availability of substances like ammonium dinitramide in requisite quantities besides the cost effectiveness. The phase transitions and initial endothermic decomposition of ammonium nitrate, however, pose problems in its application in composite solid rocket propellants. The influence of pressure on phase transitions, melting and thermal decomposition characteristics of AN is required to be systematically studied in order to have an insight in the combustion mechanism of AN containing propellants. Pressure differential scanning calorimetric (PDSC) studies have consequently been conducted on pure AN under ambient conditions and upto a maximum inert pressure of 68.03 atm. The shifts in the phase transition peaks, melting and decomposition temperatures with pressure have been studied. It has been observed that thermal decomposition of AN remains an endothermic process upto a prepare of 20.41 atm and thereafter becomes exothermic in nature. Phase transitions, melting and decomposition processes are found to be pressure sensitive and the associated peaks register a positive temperature shift bearing a relationship with crystal structure in two distinct pressure segments corresponding to endo- and exothermic decomposition.

Thermotropic phase behaviour of α-dipalmitoylphosphatidylcholine multibilayers is influenced to various extents by carotenoids containing different structural features- evidence from differential scanning calorimetry

Carotenoids are the effective modulators of physical properties of model and natural membranes. To demonstrate the relationship between the structure of carotenoids and their effect on the molecular dynamics of membranes, we have investigated the influence of five structurally different carotenoids: β-carotene, lycopene, lutein, violaxanthin, zeaxanthin and additionally carotane- a fully saturated derivative of β-carotene, on thermotropic phase behaviour of dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles by means of differential scanning calorimetry (DSC). The results obtained indicate that the carotenoids used modulated the thermotropic properties of multibilayers to various extents, broadening the pretransition and the main phase transition peaks and shifting them to lower temperatures. Pronounced decrease of pretransition enthalpy (ΔHp) proves that carotenoids very strongly alter the membrane properties in its gel phase. Comparison of the influence of several carotenoids shows that a rigid, polyisoprenoid chain plays a basic role in altering the thermotropic properties of such membranes and the presence of rings without oxygen-containing groups has a minor significance for the observed interactions. Carotenoids containing epoxy and/or hydroxy groups attached to their rings modify the thermotropic phase behaviour of DPPC multilamellar vesicles stronger than carotenes- a result of their orientation in the DPPC bilayer.

MgO-mixed Ba0.6Sr0.4TiO3 bulk ceramics and thin films for tunable microwave applications

The dielectric properties of Ba0.6Sr0.4TiO3 (BST) and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST bulk ceramics and thin films were investigated for tunable microwave applications. The effects of MgO mixing with BST on BST phase transitions were examined. It is observed that Mg substitution into BST causes a shift in the cubic-tetragonal BST phase transition peak to a lower temperature. Mg-substituted BST and MgO-mixed phases exhibit depressed and broadened BST phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. BST and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST thin films (∼0.3 μm thick) were deposited on (100) MgO single-crystal substrates at 750°C in an oxygen ambient pressure of 200 mTorr by pulsed laser deposition. The MgO–BST composite thin films showed a relatively high dielectric Q (=1/tan δ) compared to the pure BST and Mg-substituted BST thin films while retaining useful dielectric tuning.

Damping Behavior and Mechanism of Foamed Zn-Al Eutectoid Alloy

The present work investigates the damping behavior and mechanisms in foamed Zn–Al eutectoid alloy prepared by air pressure infiltration process. Pores in the foamed Zn–Al eutectoid alloy have macroscopic size of the order of a millimeter (0.5–1.0 mm) and in large proportions, typically up to 65 vol%. The damping behavior of the foamed Zn–Al eutectoid alloy is characterized by internal friction (IF). IF and relative dynamic modulus measurements at maximum surface shear strain of 20 × 10—6 have been made using a multifunction internal friction apparatus (MFIFA) at three discrete frequencies of 0.5, 1.0, and 3.0 Hz over a temperature range from room temperature to 400 °C, while continuously changing temperature. Two IF peaks were found in the IF–temperature curves. The first is a grain boundary IF peak, which is associated with the diffusive flux on a crystalline boundary of Al. Its activation energy has been calculated to be (1.12 ± 0.04) eV and the pre-exponential factor τ0 is 10—14 s in IF measurements. The second is a phase transition peak, which results from the transformation of Zn–Al eutectoid. Experimental results show that this phase transition IF peak is a function of Ṫ/f (Ṫ rate of temperature change, f vibration frequency), but is not proportional to Ṫ/f. Finally, the damping capacity of the foamed Zn–Al eutectoid alloy, with different macroscopic pore volume fractions and two different macroscopic pore sizes, were compared with that of bulk Zn–Al eutectoid alloy specimens. The damping capacity of the materials is shown to increase with increasing volume fraction of macroscopic pores and increase with decreasing macroscopic pore size. The operative possible damping mechanisms in the foamed Zn–Al eutectoid alloy were discussed in light of IF measurements.

Phase transition behaviors of BaTiO3–BaZrO3 solid solutions under high direct current bias fields

The dielectric properties of the Ba(Ti1–xZrx)O3 (BT1–xZx) ceramics with various compositions were investigated under various DC bias fields. In BT0.94Z0.06 ceramics, the dielectric constants (ε) vs temperature (T) curves without DC bias showed no frequency dependence. Its DC bias dependence exhibited that with increasing DC bias fields, the dielectric constants were suppressed while phase transition peaks slightly shifted to high temperature. In BT0.58Z0.42 ceramics, the ε vs T curves without DC bias showed a broad peak with a clear frequency dependence, which revealed that BT0.58Z0.42 ceramics were the relaxor. Its DC bias dependence exhibited that with increasing DC bias fields, the dielectric constants were suppressed while the phase transition peak largely shifted to low temperatures. In BT0.79Z0.21 ceramics, the ε vs T curves without DC bias showed a broad peak without frequency dependence. Its DC bias dependence revealed that the dielectric peak shifted to high temperature and broadened with increasing DC bias. To explain the above phenomena, it was considered that the role of Zr ions on BT1−xZx ceramics is to make the depth of the potential well shallow successively.

Effects of Ca doping on the oxygen ion diffusion and phase transition in oxide ion conductor La 2Mo 2O 9

The effects of Ca doping on the oxygen ion diffusion and phase transition in oxide ion conductors La 2Mo 2O 9 has been investigated by low frequency internal friction measurement and X-ray diffraction. It is found that the two relaxation subpeaks at lower temperature, which are associated with the oxygen ion diffusion, and the phase transition peak at higher temperature were affected seriously by Ca doping. With the increase of Ca doping content, the peak height of the relaxation peak decreases, but the activation energy increases at first and then decreases. From the influence of Ca doping on the peak height and activation energy of the relaxation peaks, it is deduced that Ca doping can make the oxygen ion diffusion easier in some doping content. As for the phase transition around 833 K, substituting La 3+ cation in some degree with divalent Ca 2+ can suppress it and maintain the high temperature phase to lower temperature, which help to improve the oxygen ions conducting property.

Dielectric properties anomaly of (1−x)Pb(Ni1/3Nb2/3)O3−xPbTiO3 ceramics near the morphotropic phase boundary

Dielectric properties and the phase compositions of (1−x)Pb(Ni1/3Nb2/3)O3−xPbTiO3 ceramics were investigated. A morphotropic phase boundary (MPB) in the system between pseudocubic and tetragonal phase regions has been identified to lie in the composition range x = 0.34–0.38 by means of x-ray diffraction and dielectric measurements. The samples of composition lying near the MPB have good dielectric properties, but at the same time, exhibit two dielectric peaks. The possible reasons for the occurrence of dielectric bipeaks are discussed. One dielectric peak is phase transition peak, and the other peak lying in 130–150 °C temperature range is suggested to result from structure defects in the ceramics.

Ultrathin-film differential-thermal-analysis apparatus with simultaneous photoemission measurements

We developed an apparatus of differential thermal analysis (DTA) capable of simultaneous surface specific ultraviolet (UV) photoemission measurements to investigate thin-film phase transitions. The apparatus was installed in a vacuum chamber of 10−6 Torr range for thermal isolation and the measurements of UV photoemission. As a sample substrate, we used a thin (10 μm) copper sheet supported by two wires for optimal thermal resistivity. The performance of the apparatus was examined using a 650-Å-thick pentacontane (n-C50H102) film, which may exhibit a unique monolayer phase transition known as surface freezing. We observed two anomalies of DTA curve around the bulk melting temperature, one of which is apparently due to the bulk melting. Since the temperature dependence of the surface specific UV photoemission measurements showed corresponding changes in photoemission current, we could conclude that the other phase transition peak originates from the surface freezing effect. This demonstrates that our DTA-UV apparatus is sufficiently sensitive to examine such monolayer phase transitions.

Differential thermal analysis and ultraviolet photoemission study on the surface freezing effect of n-alkane

Abstract We have performed differential thermal analysis (DTA) and surface-specific ultraviolet (UV) photoemission measurements to investigate the surface freezing effect of n -alkanes. The samples used in the experiments were pentacontane ( n -C 50 H 102 : 650 A) and tetratetracontane ( n -C 44 H 90 : 600A) films evaporated on a copper substrate. We have observed a monolayer phase transition by DTA and proved that the transition is of first order. Since the temperature dependence of the surface-specific UV photoemission measurement showed a stepwise increase and decrease of the photoemission current at the transitions observed in DTA, we could conclude that the monolayer phase transition peak originates from the surface freezing effect.

Interaction of the GM2-activator protein with phospholipid-ganglioside bilayer membranes and with monolayers at the air-water interface.

Differential scanning calorimetry (DSC) and film balance measurements were performed to study the interactions of the GalNAcbeta1-->4(NeuAcalpha2-->3)Galbeta1-->4Glc1 -->1'Cer (GM2)-activator protein with phospholipid/ganglioside vesicles and monolayers. The nonglycosylated form of the GM2-activator protein, added to unilamellar lipid vesicles of different composition, causes differential effects on the gel to liquid-crystalline phase transition peaks. The phase transition temperature (Tm) of pure dimyristoylglycerophosphocholine (DMPC) bilayer is slightly decreased. When lipids which specifically bind the GM2-activator protein are incorporated into the vesicles (e.g. a sulfatide or gangliosides) a shoulder in the thermograms at higher temperatures is observed, indicating an increase of the stability of the gel phase in relation to the liquid-crystalline phase. We also studied the surface activity of a glycosylated and a nonglycosylated GM2-activator protein at the air-water interface. The glycosylated form showed a slightly lower surface activity than the GM2-activator protein without oligosaccharide moiety. When the GM2-activator protein is added to the sub-phase of a surface covered with a lipid monolayer, it can only insert into the monolayer and reach the air-water interface below a monolayer pressure of 25 mN.m-1, depending on the lipid composition, and not when the monolayers are at the bilayer equivalence pressure of 30-35 mN.m-1. Particularly for Galbeta1-->3GalNAcbeta1-->4(NeuAcalpha2-->3)Galbeta 1-->4Glc1-->1'Cer (GM1) and GM2 containing films, the critical pressures (picrit) when no additional increase in surface pressure is observed after addition of the protein into the subphase, are much lower. This leads to the conclusion that binding of the GM2 activator protein to the ganglioside headgroups prevents the protein from reaching the air-water interface. The protein is then located preferentially at the lipid-water interface and cannot penetrate into the chain region.

A differential thermal analysis and ultraviolet photoemission study on surface freezing of n-alkanes

The surface-freezing effect of pentacontane ( n-C 50H 102) and tetratetracontane ( n-C 44H 90) films evaporated on a copper substrate has been investigated by differential thermal analysis (DTA) simultaneously with measurements of surface-specific ultraviolet (UV) photoemission. Two anomalies in the DTA curve were observed near the bulk melting temperature, one of which has been attributed to bulk melting. Since the temperature dependence of the surface-specific UV photoemission measurement showed a corresponding stepwise increase and decrease in the photoemission current at the two anomalies observed in the DTA, we have concluded that the other phase transition peak originates from surface freezing.

Surface polyfluorinated cationic vesicles

Three novel polyfluorinated cationic surfactants having a short perfluoroacyl group and double long alkyl chains, and three corresponding hydrocarbon analogues were synthesized. All of the surfactants formed small unilamellar vesicles in water upon sonication. The temperature conditions for the sonication were carefully determined by confirming that the DSC curve had a reproducible single phase transition peak. The TEM images indicated that the size of the polyfluorinated vesicles was in the range of 56–89 nm. The NMR relaxation study upon the addition of paramagnetic Mn2+ ions to the bulk water phase showed that the terminal trifluoromethyl group of the short acylamide chain in the surfactants faced directly to the bulk water phase; the vesicle had a unique micro-structure with the perfluoroalkyl group extending its arm straightforwardly to the water phase. The vesicles were named '‘surface polyfluorinated vesicles’'. The local oxygen concentrations surrounding each fluorine nucleus and proton of the surfactants within the vesicles were estimated by observing the longitudinal relaxation time under nitrogen and oxygen atmospheres. Oxygen was enriched in the microenvironment surrounding the long alkyl chain and perfluoralkyl group, while the N-methyl group had a low oxygen concentration around it. The micro-distribution of water within the vesicle was discussed by the estimated local concentration of oxygen. The vesicles were thought to be stabilized by the channel-like water connecting the bulk water phase with the hydrated water of the N-methyl groups inside the vesicles. The surface polyfluorinated layer exhibited a substantial protective effect against the oxidative attack of hydroxyl radical generated in the bulk phase water.