Lattice Elongation Research Articles

Obvious phase transition status induced by He+-ions implantation in KTN crystal

We report on the formation of a critical ferroelectric state induced by the He+ ion implantation in potassium tantalate niobate crystal. Obvious phase change has been observed in the ion irradiated region, which is mostly related to the stable polarized nanometric regions formed during the ion implantation process. Under the irradiation of 2 MeV He+ ions, two distinguishable layers corresponding to different energy transfer modes (elastic nuclear collision and inelastic electronic collision, respectively) between the incident He+ ions and the intrinsic lattices have been formed beneath the irradiated surface. Lattice dynamics before and after the ion implantation process are investigated by the confocal µ-Raman system. And the variations of typical Raman-active vibrational modes demonstrate the presence of lattice distortion in the irradiated region. X-ray diffraction experiments further suggest the mostly uniform lattice elongation in this region. Piezo-response force characteristic measurements reveal the existence of stable polarized nanometric regions with more intense polarization and verify that the crystal with such a phase status possesses extraordinary microscopic disorders, which is different from the traditional ferroelectric or paraelectric phase. Optical transmission experiments demonstrate that the irradiated region possesses relatively low propagation loss. The ion implantation method provides a new approach to form a temperature-stable critical ferroelectric state in relaxor ferroelectric materials. Analyses of the modification on the lattice dynamics of the irradiated region can help us build a clear awareness of the physical essence of this critical state and the relaxor ferroelectricity. Also, with good optical transmittance, the irradiated region is capable of promising optical functional devices.

Quantum paraelectric phase of SrTiO3 from first principles

We demonstrate how the quantum paraelectric ground state of ${\mathrm{SrTiO}}_{3}$ can be accessed via a microscopic ab initio approach based on density functional theory. At low temperature the quantum fluctuations are strong enough to stabilize the paraelectric phase even though a classical description would predict a ferroelectric phase. We find that accounting for quantum fluctuations of the lattice and for the strong coupling between the ferroelectric soft mode and lattice elongation is necessary to achieve quantitative agreement with experimental frequency of the ferroelectric soft mode. The temperature dependent properties in ${\mathrm{SrTiO}}_{3}$ are also well captured by the present microscopic framework.

Enhancing Hydrogen Cluster Storage in Clathrate Hydrates via Defect-Mediated Lattice Engineering

Can we create even more “plenty of room at the bottom” of the confined nanospaces in clathrate hydrates by tuning the complex interactions between the host water frameworks and guest molecules? Because the lattice of the clathrate hydrate is stabilized by van der Waals forces between the host and guest, irradiating the lattice of the clathrate hydrate with energetic particles is anticipated to introduce artificial defects on the host water molecules, resulting in creating a better occupation of guest molecules. Here, we explored the effects of proton irradiation on the intermolecular hydrogen and intramolecular polar covalent bonds in the host frameworks of THF hydrates. The distinct roles of the secondary guest molecules in the lattice elongation of the proton irradiated THF hydrates were examined experimentally. Conclusively, multiple occupations of H2 in small cages was observed at moderate pressure and temperature conditions following H2 reloading of the lattice elongated THF hydrate.

Obvious Phase Transition Status Induced by He <sup>+</sup>-Ions Implantation in KTN Crystal

We report on the formation of a critical ferroelectric state induced by the He+ ion implantation in potassium tantalate niobate crystal. An obvious phase change has been observed in the ion irradiated region, which is mostly related to the stable polarized nanometric regions formed during the ion implantation process. Under the irradiation of 2 MeV He+ ions, two distinguishable layers corresponding to different energy transfer modes (elastic nuclear collision and inelastic electronic collision, respectively) between the incident He + ions and the intrinsic lattices have been formed beneath the irradiated surface. Lattice dynamics before and after the ion implantation process are investigated by a confocal μ-Raman system. And the variations of typical Raman-active vibrational modes demonstrate the presence of lattice distortion in the irradiated region. X-ray diffraction experiments further suggest the uniform lattice elongation in this region. Piezo-response force characteristic measurements reveal the existence of stable polarized nanometric regions with more intense polarization and verify that the crystal with such a phase status possesses extraordinary microscopic disorders, which is different from the traditional ferroelectric or paraelectric phase. The ion implantation method provides a new approach to form a temperature-stable critical ferroelectric state in relaxor ferroelectric materials. Also, analyses of the modification on the lattice dynamics of the irradiated region can help us build a clear awareness of the physical essence of this critical state and the relaxor ferroelectricity.

Magnetic, magnetocaloric effect and resistivity behavior of Sb substituted MnAs

Magnetic, magnetocaloric effect and resistivity behavior of phase pure MnAs1−xSbx systems, synthesized by solid state reaction, have been studied for x up to 0.3. The systems display ferromagnetic metal to paramagnetic insulator transition and the transition temperature TC systematically decreases with increase in x. Arrot plot analysis indicate that the magnetic transition is of first order for all the samples though thermal hysteresis about TC is observed only for x up to 0.15. Isothermal magnetization measurements have been performed in four different protocols traversing distinctive thermodynamic paths and the isothermal magnetic entropy changes (ΔS) have been estimated using Maxwell thermodynamic equation. ΔS(T) exhibit similar asymmetric peak behavior for samples in the range 0.1–0.3 about the corresponding TC both in shape and magnitude, where as x = 0.05 sample exhibits sharp peak followed by a plateau for field change ΔH in the range 10–70 kOe. The value of extracted ΔS(T) is independent of the measurement protocol within the estimated error for all the samples. The calculated refrigeration capacity for two considered cases of hot and cold sink temperatures, viz. TC – 25 and TC + 25 K and temperatures at the full width half maximum is found to be same in all the samples for any ΔH in the range 10–70 kOe. Resistivity behavior in ferromagnetic region manifests contribution from electron-magnon scattering following T2 dependence and electron-phonon contribution following Bloch-Grüneisen formalism. Our analysis indicates lattice elongation is responsible for reduction in TC and Debye temperature ΘD. It is surmised that enhanced spin fluctuations are responsible for paramagnetic insulating behavior.

Incorporated Guanidinium Expands the CH3NH3PbI3 Lattice and Enhances Photovoltaic Performance.

Guanidinium (GA) has been widely used as an additive in solar cells for enhanced performance. However, the size of the guanidinium cation is too large to be incorporated in the cage of the perovskite structure. Instead, GA forms a variety of structures with lead iodide, where its role in the perovskite crystal as well as solar cell devices is unclear. In this study, we demonstrate that GA can be incorporated into the structure of MAPbI3 as (GA)x(MA)1-xPbI3. From single-crystal X-ray crystallographic refinement, we observe lattice expansion and Pb-I bond elongation with GA incorporation similar to exerting "negative pressure", which weakens orbital overlap and widens the band gap from 1.49 to 1.53 eV. We find that the highest percentage of GA that can be incorporated into the 3D MAPbI3 structure is 5.26%, as confirmed by nuclear magnetic resonance. The alloyed (GA)x(MA)1-xPbI3 exhibits increased PL lifetimes from 154.4 to 266.3 ns after GA incorporation while the Voc of (GA)x(MA)1-xPbI3 devices enlarges from 1.05 to 1.11 V. High efficiencies in solar cell devices up to 20.38% with a Jsc of 23.55 mA cm-2, Voc of 1.11 V, and FF of 0.78 have been achieved, with stable photovoltaic performance for 900 h in air.

Ferroelastic domain motion by pulsed electric field in (111)/(111¯) rhombohedral epitaxial Pb(Zr0.65Ti0.35)O3 thin films: Fast switching and relaxation

Reversible electric-field induced domain switching in ferroelectric thin films gives rise to a large electromechanical coupling. Despite extensive in situ studies confirming a dominant contribution from domain switching, the speed of the domain wall motion had not been discussed enough. In this study, we performed time-resolved measurement of lattice elongation and non-180\ifmmode^\circ\else\textdegree\fi{} domain switching for an epitaxial rhombohedral $(111)/(11\overline{1})$-oriented ($\mathrm{Pb}(\mathrm{Z}{\mathrm{r}}_{0.65}\mathrm{T}{\mathrm{i}}_{0.35}){\mathrm{O}}_{3}$ film under nanosecond electric field pulses by means of synchrotron x-ray diffraction. Both lattice elongation and non-180\ifmmode^\circ\else\textdegree\fi{} domain switching due to a 200-ns electric pulse were directly observed from the shift of the 222 diffraction position toward a lower angle and the change in the integrated intensity ratio of 222 to $22\overline{2}$ peaks, respectively. The non-180\ifmmode^\circ\else\textdegree\fi{} domain switching also results in an increase of the switchable polarization. Following the removal of the electric field, it is seen that the non-180\ifmmode^\circ\else\textdegree\fi{} domain back switching from 222 to $22\overline{2}$ is sluggish compared to the relaxation of the field-induced lattice strain. This is different from the (100)/(001)-oriented tetragonal epitaxial $\mathrm{Pb}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_{3}$ films, in which no obvious delay was detected. These results show the importance of the direct time-resolved response observation of the crystal structure change with the application of a high-speed electric pulse field to understand the frequency dispersion of the ferroelectric and piezoelectric responses of $\mathrm{Pb}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_{3}$ films.

Electric field-induced change in the crystal structure of MOCVD-Pb(Zr,Ti)O3 films near the phase boundary

The change in the crystal structure after poling and under an constant electric field was investigated for Pb(ZrxTi1-x)O3 films. The preparation of approximately 1.5 μm thick (100)T/(001)T/(100)R-oriented Pb(ZrxTi1-x)O3 films with a Zr/(Zr + Ti) ratio of 0.54–0.67 took place on (100)CSrRuO3/(100) CLaNiO3/(111)Pt/TiO2/SiO2/Si substrates by pulsed metal organic chemical vapor deposition. Increasing Zr/(Zr + Ti) ratio provides a change in the constituent phases of the films from single-phase tetragonal to a mixture of tetragonal and rhombohedral phases, and finally, to single-phase rhombohedral. The crystal structure of all films changed after the poling process and under an electric field in various ways according to the Zr/(Zr + Ti) ratios of the films; including lattice elongation, domain switching, and phase change. In particular, a single peak from the rhombohedral phase is asymmetrically broadened by both the poling process and an applied electric field suggesting that a (100)-oriented rhombohedral phase presumably changed to a (001)-oriented tetragonal phase.

Effect of Nd doping on the refractive index and thermo-optic coefficient of GdVO4 single crystals

Undoped and Nd (0.2, 0.6, 0.8, 1.0, 1.2 and 1.6 at%)-doped GdVO4 single crystals have been grown by optical floating zone technique. XRD analysis reveals small lattice expansion especially along c axis on Nd doping. It has been observed that the extra-ordinary refractive index (RI) of undoped GdVO4 crystals is higher than the doped GdVO4 single crystals up to 1.0 at% Nd doping, beyond which it surpasses the value of the undoped crystal. This is due to the competing effect of lattice elongation and decrease in electron density on Nd doping. The increase in RI with Nd doping is attributed to macroscopic polarization effects. Moreover, the extra-ordinary refractive index (ne) only increases on increasing Nd concentration, whereas ordinary refractive index (no) remains unaffected within the measurement limits. The temperature-dependent RI measurements depicted a positive thermo-optic coefficient (TOC) for RI and birefringence, which is ~ 10−5/°C and is independent of doping concentration. TOC for ne is higher than no, which has been explained on the basis of anisotropic thermal expansion. An important set of relations between TOC and wavelength (532–1551 nm) has been established which is useful for estimating TOC in the temperature range of 30–150 °C.

Electric field induced phase transition and accompanying giant poling strain in lead-free NaNbO3-BaZrO3 ceramics

A series of phase transitions in (1-x)NaNbO3-xBaZrO3 ((1-x)NN-xBZ) ceramics was observed from antiferroelectric orthorhombic phase to ferroelectric orthorhombic phase and finally into ferroelectric rhombohedral phase with increasing x. An electric field induced irreversible phase transition was found in different compositions, irrespective of their virgin phase structures. Particularly, an antiferroelectric orthorhombic phase is irreversibly transformed into a ferroelectric monoclinic phase within 0.02 ≤ x ≤ 0.05, leading to a giant poling strain of ∼0.58%. This is much larger than that observed in ferroelectric orthorhombic (0.06 ≤ x ≤ 0.07) and rhombohedral phases (0.08 ≤ x ≤ 0.11) suffering from an irreversible ferroelectric-ferroelectric (monoclinic) phase transition. The synchrotron x-ray diffraction and the measurement of longitudinal and transverse strains suggest that this irreversible phase transition should involve not only a distinct volume expansion, but also an obvious lattice elongation. The present study demonstrates a unique nature of the composition and field dependent phase stability and an underlying mechanism of giant poling strains in NN-BZ ceramics.

Electric field induced irreversible change and asymmetric butterfly strain loops in Pb(Zr,Ti)O3-Pb(Ni1/3Nb2/3)O3-Bi(Zn1/2Ti1/2)O3 quaternary ceramics

The phase transformation and strain characteristics of (0.9-x)Pb(Zr0.54Ti0.46)O3−0.1Pb(Ni1/3Nb2/3)O3-xBi(Zn1/2Ti1/2)O3 (0.1PNN-(0.9-x)PZT-xBZT) solid-solution ceramics were investigated. The substitution of BZT for PZT can effectively decrease the sintering temperature from 1150 °C at x = 0–975 °C at x = 0.24. A typical morphotropic phase boundary (MPB) between ferroelectric rhombohedral (R) phases and relaxor tetragonal (T) phases was identified in the composition range of x = 0.12–0.18, resulting in enhanced dielectric, piezoelectric and electromechanical properties of d33 = 610 pC/N, kp = 58% an ε33T/εo = 2518 at x = 0.16. Most interestingly, exceptionally asymmetric butterfly strain loops were observed in the first-cycle electric loading, and found to obviously change with increasing the BZT content. The X-ray diffraction analysis on virgin and poled samples suggests that the observed asymmetric strain curves should stem from the electric field induced irreversible lattice shrinkage or lattice elongation in the single-R or single-T phase compositions, respectively. For MPB compositions, a combined effect of both opposite strain contributions would result in a maximum value (in absolute value) in the observed irreversible strain Sirr at x = 0.12, together with the effect of the electric field induced irreversible T-R phase transition. These results provide useful insights into the mechanism of forming asymmetric bipolar strains observed in BZT-substituted PZT-PNN piezoelectric ceramics.

Elasto-optic behaviour in epitaxial films of perovskite oxide ferroelectrics

ABSTRACTLarge variations of refractive index in the visible spectral range are obtained in epitaxial perovskite oxide ferroelectric films experiencing lattice strain. The strain is imposed by substrates, on top of which the films are grown. The optical constants are determined using the spectroscopic ellipsometry. As a reference and for comparison, also prototype single crystals are inspected. The variations in refraction are related to the lattice strain in the films. Elasto-optic coefficient is formally estimated using the out-of-plane lattice elongation or shrinkage in the films compared to bulk. The obtained elasto-optic coefficients exceed significantly those previously reported for ferroelectric materials.

Magnetic properties of ultrathin tetragonal Heusler D22-Mn3Ge perpendicular-magnetized films

We investigated the crystal structure and magnetic properties of Manganese-germanium (Mn3Ge) films having the tetragonal D022 structure, with varied thicknesses (5–130 nm) prepared on chromium (Cr)-buffered single crystal MgO(001) substrates. A crystal lattice elongation in the in-plane direction, induced by the lattice mismatch between the D022-Mn3Ge and the Cr buffer layer, increased with decreasing thickness of the D022-Mn3Ge layer. The films exhibited clear magnetic hysteresis loops with a squareness ratio close to unity, and a step-like magnetization reversal even at a 5-nm thickness under an external field perpendicular to the film's plane. The uniaxial magnetic anisotropy constant of the films showed a reduction to less than 10 Merg/cm3 in the small thickness range (≤20 nm), likely due to the crystal lattice elongation in the in-plane direction.

Strain glass transition in a multifunctional β-type Ti alloy

Recently, a class of multifunctional Ti alloys called GUM metals attracts tremendous attentions for their superior mechanical behaviors (high strength, high ductility and superelasticity) and novel physical properties (Invar effect, Elinvar effect and low modulus). The Invar and Elinvar effects are known to originate from structural or magnetic transitions, but none of these transitions were found in the GUM metals. This challenges our fundamental understanding of their physical properties. In this study, we show that the typical GUM metal Ti-23Nb-0.7Ta-2Zr-1.2O (at%) alloy undergoes a strain glass transition, where martensitic nano-domains are frozen gradually over a broad temperature range by random point defects. These nano-domains develop strong texture after cold rolling, which causes the lattice elongation in the rolling direction associated with the transition upon cooling and leads to its Invar effect. Moreover, its Elinvar effect and low modulus can also be explained by the nano-domain structure of strain glass.

Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3

We report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastic a–c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a–c domain pattern in the Fe films. Exchange and magnetostatic interactions between neighboring magnetic stripes further influence magnetization reversal and pattern formation within the a and c domains.

Effect of Substrate Strain and Interface on Magnetic Properties of EuTiO3 Thin Film

ABSTRACTBulk EuTiO3 is known as a compound in which spin and soft phonon mode is strongly coupled. Recent theoretical study suggests that application of stress or formation of strain leads to a drastic change in magnetic and dielectric properties of EuTiO3 and that so-called multiferroic properties emerge under such a situation. In the present study, effect of strain induced by a substrate, on which EuTiO3 thin film is deposited, on the magnetic properties of the film has been experimentally examined. By using a pulsed laser deposition method, EuTiO3 thin film has been deposited on different kinds of substrate, i.e., LaAlO3, SrTiO3, and DyScO3; the lattice parameter of these compounds is smaller than, just the same as, and larger than that of EuTiO3, respectively. X-ray diffraction analysis confirms that the strain induced in the plane of as-deposited EuTiO3 thin films on different substrates is coincident with the lattice parameter of the substrate compounds. Also, all the as-deposited EuTiO3 thin films manifest elongation of lattice in a direction perpendicular to the film surface. Temperature dependence of magnetization indicates that all the thin films exhibit ferromagnetic behavior at low temperatures. The magnetization at 2 K under a magnetic field of 100 Oe is the highest for EuTiO3 on DyScO3 and the lowest for EuTiO3 on LaAlO3. The experimental result is coincident with the first-principles calculations which predict that ferromagnetic spin configuration becomes more stable as the lattice volume of EuTiO3is increased.

A Molecular Dynamics Study of an hcp-to-fco Martensitic Transformation and Its Crystallographic Correlation in a Ti Lattice, upon Dissolution of Cu Atoms

A hexagonal close-packed to face-centered orthorhombic (hcp-to-fco) transformation in a Ti lattice, upon dissolution of Cu atoms, is observed by molecular dynamics simulations based on a proven realistic many-body Cu–Ti potential. It was found that the phase transformation takes place through two main simultaneous actions, i.e., lattice elongation along the close-packed directions and relative movement or slide between adjacent close-packed planes along the directions. By analyzing the crystallographic relationship between the hcp, bcc (body-centered cubic), and fco structures, it is proposed that the phase transformation occurs through a reverse mechanism, for the body-centered cubic to hexagonal closed-packed (bcc-to-hcp) phase transformation, together with lattice constant adjustments.

Investigations on the defect structure and the EPR parameters for AgBr:Ir2+

The defect structure and the EPR parameters (the g factors, the hyperfine structure constants and the superhyperfine parameters) for the tetragonal Ir(2+) center in AgBr are theoretically investigated using the perturbation formulas of these parameters for a 5d(7) ion in tetragonally elongated octahedra. In the calculations, the contributions from the ligand orbital and spin-orbit coupling interactions and the local lattice (elongation) distortion due to the Jahn-Teller effect are taken into account. Related molecular orbital coefficients and the ligand unpaired spin densities are determined quantitatively using a cluster approach. The impurity center is attributed to the substitutional [IrBr(6)](4-) cluster on host Ag(+) site, which suffers the relative elongation of about 0.08 angstrom along C(4) axis due to the Jahn-Teller effect. The calculated EPR parameters based on the above Jahn-Teller elongation show good agreement with the observed values.

Mechanical stretching effect on the actuator performance of cellulose electroactivepaper

The mechanical stretching effect on the actuating performance of electroactive cellulosepaper (EAPap) was studied. A lattice elongation of cellulose fibrils due to in-plane tensilestress along the stretching direction was observed by the x-ray diffraction method. Theshrinkage of the fibril diameter as a function of stretching ratio was confirmed by surfaceand cross-sectional images. While the actuator performance in terms of bendingdisplacement decreased as the stretching ratio increased, the resonance frequency linearlyincreased as the stretching ratio increased, which was compared with the theoreticalfrequency data found from a cantilever beam model. The actuator efficiency was evaluatedfrom the electrical input power consumption and the mechanical output power ofan EAPap actuator. It was revealed that the stretching process increased theelectro-mechanical efficiency of the EAPap actuator. The mechanism of the influenceof the stretching effect on the performance of an EAPap actuator is discussed.

Aplicação de programa de análise de imagens na interpretação de fotomicrografias de alta resolução de argilominerais

O objetivo principal deste trabalho é destacar o potencial da análise de imagens na interpretação de fotomicrografias de argilominerais. Foram usadas imagens de argilas obtidas com um microscópio eletrônico de transmissão de alta resolução e um programa de análise de imagens. A manipulação das imagens, usando as diferentes ferramentas do programa, permite melhorar sua qualidade e quantificar alguns parâmetros importantes, tais como a morfologia estrutural dos diferentes compostos, os espaçamentos interplanares e o ângulo de inclinação das franjas de rede, o tamanho e a morfologia de grãos do material, dentre outras medidas de interesse. Foram aplicados diversos filtros para melhorar a imagem inicial e a transformada rápida de Fourier foi aplicada em imagens individuais de grãos que apresentam franjas de rede. Além desses filtros, o programa tem outras ferramentas que podem ser usadas para fazer medidas (de diâmetros, áreas, comprimentos etc.), que permitem determinar distâncias interplanares dos planos (hkl) selecionados. Embora o programa possa ser usado em outras aplicações interessantes (por exemplo, em análise metalográfica de fotografias obtidas com microscópio óptico), neste trabalho são mostrados os resultados obtidos na análise de algumas franjas de rede de argilominerais.