Orthorhombic Phase Transformation Research Articles

In situ grazing incidence synchrotron x-ray diffraction studies on the wakeup effect in ferroelectric Hf0.5Zr0.5O2 thin films

The discovery of ferroelectricity in HfO2 ultrathin films has gathered considerable interest from the microelectronic industry owing to their compatibility with complementary metal oxide semiconductor technology. However, a significant challenge in utilizing HfO2 thin films for commercial devices is the wakeup effect, which is an increase in polarization with the number of electric field cycles in HfO2-based capacitors. Despite efforts to develop wakeup-free HfO2 thin films, the root cause of this effect remains elusive. Some studies attribute it to the tetragonal (T) to orthorhombic (O) phase transformation, while others suggest it is due to the redistribution of oxygen vacancies within the HfO2 layer during electric field cycling. This study investigated the phase transformation dynamics and oxygen vacancy distributions in TiN/Hf0.5Zr0.5O2/TiN capacitors subjected to electric field cycling using in situ grazing incidence synchrotron x-ray diffraction and ex situ x-ray photoelectron spectroscopy. The as-grown HZO films were crystallized in a mixed phase consisting of monoclinic (M), tetragonal, and orthorhombic fractions. The T-phase volume fraction decreased continuously up to 10k electric field cycles. In contrast, the O-phase fraction increased within the first 100 cycles and then stabilized with further cycling. The redistribution of oxygen vacancies occurred continuously throughout the cycling process. The results revealed that continuous oxygen vacancy redistribution during electric field cycling resulted in phase transformation between the T-, O-, and M-phases. The study provides insight into the phase transformation dynamics and oxygen vacancy redistribution in TiN/Hf0.5Zr0.5O2/TiN capacitors during electric field cycling, shedding light on the underlying mechanisms of the wakeup effect.

Role of polarization switching and domain patterns in the enhanced piezoelectric characteristics of a Pb-free ferroelectric system

The Pb-free piezoelectric BaTi1−x Sn x O3 system is a promising environmentally friendly ceramic due to its superior piezoresponse properties. The enhanced piezoresponse of this system has a strong correlation with its microscopic and macroscopic characteristics. In this work, the effects of structural and microstructural evolution on the piezoelectric properties of a BaTi0.97Sn0.03O3 (BST) compound are explored. Structural and piezoelectric analysis elucidates that the samples experiencing a field induced tetragonal to orthorhombic phase transformation exhibit better piezoresponse. In addition, the domain configurations have a strong correlation with the synthesis conditions, where the distribution of lamellar and/or stripe types of domain patterns show enhancement in comparison to those of labyrinth type with increase in sintering temperature. Rayleigh analysis confirms that the increase in the irreversible nature of non-180° domain walls can improve the d 33 values of the BST samples. Overall, the results illustrate that the stripe domain configurations and field induced polarization switching from tetragonal to orthorhombic phase favour superior piezoresponse in the samples.

The α2 to orthorhombic phase transformation facilitated high elastically mediated strain transfer ability in high Nb-TiAl alloys

The α2 to orthorhombic phase transformation facilitated high elastically mediated strain transfer ability in high Nb-TiAl alloys

Impact of Pt grain size on ferroelectric properties of zirconium hafnium oxide by chemical solution deposition

The effects of the grain size of Pt bottom electrodes on the ferroelectricity of hafnium zirconium oxide (HZO) were studied in terms of the orthorhombic phase transformation. HZO thin films were deposited by chemical solution deposition on the Pt bottom electrodes with various grain sizes which had been deposited by direct current sputtering. All the samples were crystallized by rapid thermal annealing at 700 °C to allow a phase transformation. The crystallographic phases were determined by grazing incidence X-ray diffraction, which showed that the bottom electrode with smaller Pt grains resulted in a larger orthorhombic phase composition in the HZO film. As a result, capacitors with smaller Pt grains for the bottom electrode showed greater ferroelectric polarization. The smaller grains produced larger in-plane stress which led to more orthorhombic phase transformation and higher ferroelectric polarization.

Sublayer thickness dependence of nanolaminated HfO2–Al2O3 films for ferroelectric phase stabilization

In this study, to understand the effect of sublayer thickness of doped HfO2 films with limited dopant solubility on ferroelectric phase stabilization, nanolaminated HfO2–Al2O3 films with various sublayer thicknesses were prepared through atomic layer deposition (ALD), and the phase evolution behavior of these films with increasing post-metallization annealing (PMA) temperature was investigated. A narrow optimal range of the HfO2 sublayer thickness was required to achieve facile crystallization into a tetragonal phase, followed by orthorhombic phase transformation through sufficient Al diffusion. Because the Al2O3 sublayer cannot be completely dissolved, it should be as thin as possible so that it can easily agglomerate to provide an effective connection between the HfO2 sublayers during the PMA process. When stabilizing the ferroelectric phase of HfO2 films by mixing with dopants with limited solubility, the thicknesses of the HfO2 and Al2O3 sublayers in the nanolaminated form were revealed to be more critical than the nominal doping concentration inferred from their thickness ratios (ALD cycle ratios).

Influence of hexagonal to orthorhombic phase transformation on diffusion-controlled dendrite evolution in directionally solidified Sn–Ni peritectic alloy

The hexagonal to orthorhombic (HO) transformation from β-Ni3Sn2 (hexagonal) phase to α’-Ni3Sn2 (orthorhombic) phase was confirmed in directionally solidified Sn–Ni peritectic alloys. It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting (TGZM) and Gibbs−Thomson (G−T) effects can take place on secondary dendrites. Besides, the intersection angle between the primary dendrite stem and secondary branch (θ) is found to increase from π/3 to π/2 as the solidification proceeds. This is the morphological feature of the HO transformation, which can change the diffusion distance of the remelting/ resolidification process. Thus, a diffusion-based analytical model is established to describe this process through the specific surface area (SV) of dendrites. The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification. In addition, the slope of the prediction curves is changed, indicating the variation of the local remelting/resolidification rates.

Uncovering the symmetry of the induced ferroelectric phase transformation in polycrystalline barium titanate

Microstructural design is a widespread approach to tailor the properties of functional materials with the size effect being an effective constraint that modifies physical phenomena. In this work, we investigate the grain size effect on the properties and the electric field induced phase transformation behavior in barium titanate. A broad range of unimodal average grain size distribution between 0.4 and 15 μm was successfully sintered avoiding abnormal grain growth. Samples with a grain size close to the range of 1–2 μm, balancing microstructural strain, presence, and mobility of domain walls to allow the field induced crystal phase transformation, showed optimal electromechanical and dielectric properties. By means of in situ high energy x-ray diffraction and a high-resolution multianalyzer detector, we distinguish and quantify a tetragonal–orthorhombic phase transformation induced by an electric field, providing unambiguous proof of this induced phase transformation. These results contribute to the understanding of fundamental questions about the piezoelectric effect in barium titanate and consequently other similar systems.

Enhanced energy storage properties and antiferroelectric stability of Mn-doped NaNbO3-CaHfO3 lead-free ceramics: Regulating phase structure and tolerance factor

NaNbO3-based ceramics usually show ferroelectric-like P-E loops at room temperature due to the irreversible transformation of the antiferroelectric orthorhombic phase to ferroelectric orthorhombic phase, which is not conducive to energy storage applications. Our previous work found that incorporating CaHfO3 into NaNbO3 can stabilize its antiferroelectric phase by reducing the tolerance factor (t), as indicated by the appearance of characteristic double P-E loops. Furthermore, a small amount of MnO2 addition effectively regulate the phase structure and tolerance factor of 0.94NaNbO3-0.06CaHfO3 (0.94NN-0.06CH), which can further improve the stability of antiferroelectricity. The XRD and XPS results reveal that the Mn ions preferentially replace A-sites and then B-sites as increasing MnO2. The antiferroelectric orthorhombic phase first increases and then decreases, while the t shows the reversed trend, thus an enhanced antiferroelectricity and the energy storage density Wrec of 1.69 J/cm3 at 240 kV/cm are obtained for 0.94NN-0.06CH-0.5%MnO2(in mass fraction). With the increase of Mn content to 1.0 % from 0.5 %, the efficiency increases to 81 % from 45 %, although the energy storage density decreases to 1.31 J/cm3 due to both increased tolerance factor and non-polar phase.

Effect of martensite on {332} twinning formation in a metastable beta titanium alloy

{332}β twinning and stress-induced martensite transformation are two important deformation mechanisms in the metastable beta titanium alloys, which can effectively strengthen the titanium alloys via twinning induced plasticity (TWIP) and transformation induced martensite (TRIP) effect, respectively. For a TWIP + TRIP metastable beta titanium alloy, {332}β twinning and stress-induced martensite can co-exist to improve the mechanical behaviors. However, the underlying mechanism for the co-existence of {332}β twinning and stress-induced martensite is not clear. Here we employed a model metastable beta titanium alloy Ti-2Al-9.2Mo-2Fe (wt%) to reveal the correlation between {332}β twinning and stress-induced martensite. The deformation gradient analysis and magnitude of shuffling needed for twining were utilized to reveal the relationship between {332} twinning and stress-induced martensite. As a result, we found that {332} twinning is a product of the reverse bcc to orthorhombic phase transformation. Such mechanism leads to a strong correlation between {332} twinning and stress-induced martensite, causing the {332} twinning combining stress-induced martensite in the present alloy.

Elucidating the Phase Transformation and Metallization Behavior of Zinc Phosphide under High Pressure.

Among the family of II3V2-type compounds, zinc phosphide (Zn3P2) occupies a unique position. As one of the most promising semiconductors well-suited for photovoltaic applications, Zn3P2 has attracted considerable attention. The stability of its structure and properties are of great interest and importance for science and technology. Here, we systematically investigate the pressurized behavior of Zn3P2 using in situ synchrotron radiation angle-dispersive X-ray diffraction (ADXRD) and in situ electrical resistance measurement under high pressure. The ADXRD experiment shows that Zn3P2 undergoes an irreversible structural phase transition under high pressure, beginning at 11.0 GPa and being completed at ∼17.7 GPa. Consistently, the high-pressure electrical resistance measurement reveals a pressure-induced semiconductor-metal transition for Zn3P2 near 11.0 GPa. The kinetics of the phase transition is also studied using in situ electrical resistance measurement and can be well described by the classical Avrami model. What's more, the new high-pressure structure of Zn3P2 is refined to be orthorhombic with space group Pmmn; the lattice parameters and bulk modulus of this high-pressure phase are determined as a = 3.546 Å, b = 5.004 Å, c = 3.167 Å, and B0 = 126.3 GPa. Interestingly, we also predict a possible structural phase transformation of orthorhombic phase (Pmmn) to cubic phase (P4232) during the decompression process; this cubic Zn3P2 is metastable at ambient conditions. These experimental results reveal the unexpected high-pressure structural behaviors and electrical properties of Zn3P2, which could help to promote the further understanding and the future applications of Zn3P2 as well as other II3V2 compounds.

Crystallographic effects of Boron doping into Sm-Ca-Cu-O Ceramic

In this work, we have especially focused on investigating the nano Boron doping effect into the Sm-Ca-Cu-O Ceramic [1,2]. The samples produced suitable with nominal composition selected as Sm1.75 Ca (2.20-x) B x Cu 3.4 O y (x = 0.0; 0.4, 0.8 and 1.0). This effect investigated through the TG/DTA, XRD, and SEM results. Lattice parameters (a, b, and c) got from the crystallographic knowledge, and they carefully calculated. The crystallographic growth seen because of the changing at the intensity of x-ray diffraction peaks. Increasing the Boron doping in the matrix have produced the crystal growth at especially SmBP and SmB10 samples, peaks intensity at 29° (220) Miller indices, has increased from 1.602 to 10.883, respectively. Namely, with increasing B-doping resulted in a transformation of the phase. In this way (at Boron free sample) it has achieved the orthorhombic phase transformation to the tetragonal phase created in the matrix.

Strain and phase transformation co-mediated magnetoelectric effect in epitaxial Ni/PMN-PT (0 1 1) heterostructures

E-tuning of magnetic behavior is investigated in epitaxial Ni film grown on (0 1 1)-PMN-PT single crystal substrate. Loop-like and butterfly-like Hr-E and Hme-E curves are obtained along [01-1] and [1 0 0], respectively, which is mediated by the combined effects of anisotropic strain and nonvolatile rhombohedral to orthorhombic phase transformation in PMN-PT. The results are further confirmed via E-tuning of domain in PMN-PT using piezoelectric force microscope and E-tuning of magnetic stripe domain in Ni film using magnetic force microscope, as well as E-tuning of XRD. In addition, the highest E-induced Hr shift of 1253 Oe is achieved along [01-1] under electric field of −10 kV/cm. This work is of significance for the potential application in magnetoelectric multifunctional devices.

Strain rate sensitivity, microstructure variations, and stress-assisted β → α′′ phase transformation investigation on the mechanical behavior of dual-phase titanium alloys

In this study, the microstructures of three widely used dual-phase titanium alloys: Ti-6Al-4V, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-2Sn-4Zr-6Mo are characterized using backscatter electron imaging and the deformation behaviors in their individual α and β phases are investigated using in situ high-energy X-ray diffraction during uniaxial tension experiments. This is accompanied by calculation of the strain rate sensitivity (SRS) in these alloys, as a function of applied loading. The results of the calculated SRS and the mechanical response (in terms of lattice strains and hardening behaviors) are rationalized based on the local microstructure, composition, and texture of the alloy. A stress-induced β (BCC) to α" (orthorhombic) phase transformation is observed during the in-situ diffraction experiment, which permitted analysis of the lattice strain evolution during the phase transformation. Results from this study provide insights into the relationship between microstructure, composition, applied loading, and the deformation behavior, including effects on loading with time holds. Specifically, the results show that the microstructure, and not necessarily the chemical composition (Mo content), along with the applied loading have a dominant role in the observed SRS variation in titanium alloys. Also, the evolution of the α" (orthorhombic) phase is observed for the first time during deformation of an industrially relevant titanium alloy, Ti-6246.

A New Reversible Phase Transformation of Intermetallic Ti3Sn.

Ti3Sn has received increasing attention as a high damping metallic material and as an anode material for rechargeable lithium-ion batteries. However, a heated dispute concerning the existence of solid state phase transformation of stoichiometric Ti3Sn impedes its development. Here, thermal-induced reversible phase transformation of Ti3Sn is demonstrated to happen at around 300 K by the means of in-situ variable-temperature X-ray diffraction (XRD) of Ti3Sn powder, which is also visible for bulk Ti3Sn on the thermal expansion curve by a turning at 330 K. The new phase’s crystal structure of Ti3Sn is determined to be orthorhombic with a space group of Cmcm and the lattice parameters of a = 5.87 Å, b = 10.37 Å, c = 4.76 Å respectively, according to selected area electron diffraction patterns in transmission electron microscope (TEM) and XRD profiles. The hexagonal → orthorhombic phase transformation is calculated to be reasonable and consistent with thermodynamics theory. This work contributes to a growing knowledge of intermetallic Ti3Sn, which may provide fundamental insights into its damping mechanism.

Ferroelectric Properties of Si Doped HfO2 Thin Films with NiSi2 As Bottom Electrode

It has been already demonstrated that the orthorhombic phase transformation of Zr or Si doped HfO2 (induced by annealing) is responsible for its ferroelectricity but the use of capping top electrodes is usually required [1-4]. Here, we show that by using NiSi2 as bottom electrode (suggesting an orthorhombic structure after annealing), moderate ferroelectric properties of Si-doped HfO2 thin films (8.7 nm in thickness) deposited on NiSi2 electrodes can be generated during post-deposition annealing (PDA). For this Si:HfO2/NiSi2 structure, the bottom and top metallic films are deposited by sputtering at room temperature while atomic-layer deposition is used for deposition of Si:HfO2 with a cycle ratio of 1:16 (SiO2:HfO2), see figs. 1-2. Annealing in argon, forming gas and oxygen atmospheres for temperatures ranging from 1000°C down to 400°C, was done on structures having NiSi2 or TiN (used as reference) as bottom electrodes in order to correlate the influence of these processing conditions to the electrical and ferroelectric properties of the resulting MIM devices. For this, leakage current, capacitance, remanent polarization and fatigue measurements with applied voltage were obtained. Moderate ferroelectric behavior was obtained for PDA samples having NiSi2 as bottom electrode in the temperature range of 750°C–500°C, see figs. 3-4. This result shows the advantage of the use of NiSi2 bottom electrode, broadening the processing window for CMOS-compatible ferroelectric materials. AcknowledgementThis research is supported by the Center of Innovation Program from Japan Science and Technology Agency, JST.

Structural phase transition and spontaneous exchange bias in NiCr1.9Fe0.1O4 nanoparticles: XRD, EXAFS and magnetic measurements

Abstract Here, we report structural and magnetic phase transitions in NiCr1.9Fe0.1O4 nanoparticles of size ∼60 nm synthesized through cost-effective co-precipitation route. X-ray diffraction pattern shows a stable cubic phase at RT in contrast to tetragonal phase in bulk NiCr2O4. Decreasing the temperature, a complete tetragonal symmetry is observed at 50 K, while a coexistence of cubic and tetragonal phases in the intermediate temperature range. Interestingly, no tetragonal to orthorhombic phase transformation has been observed down to 12 K as observed in NiCr2O4 at 70 K. The local structure examined from temperature dependent EXAFS demonstrates that although no change in distribution of cations among tetrahedral (A) and octahedral (B) sites down to 10 K has been observed, Fe3+ ions occupy A site replacing equivalent amount of Ni2+ towards B site which is contradicting to the bulk NiCr2O4 where Ni2+ occupies only A site. Magnetic studies demonstrate a two-fold increase in para to long-range ferrimagnetic transition, TC, due to increase in A-B exchange interaction and no change in spiral ordering temperature, TS indicates strong B-B interaction. In addition, these nanoparticles exhibit unusually high spontaneous exchange bias of ∼1.265 kOe at 60 K. We discuss the temperature dependent exchange bias on the basis of competition between uncompensated B site moments and ferromagnetically ordered spins at A site. The tunable exchange bias without field highlight the potential applications of these materials in spintronics devices.

On the orientation relationships in phase transformation of CaTiO3

Abstract Electron Backscattering Diffraction (EBSD) is a well-known technique which is primarily used to analyse the microstructural features in metallic materials, including the orientation relationship between microstructural constituents. However, its versatility has not yet been critically utilized to establish crystallographic relationships involved in phase transformation of ceramics. In view of the significance of transformation twinning in ceramics on mechanical properties, the representative orientation relationships in twinned grains of CaTiO3 is investigated using EBSD. It is observed that the matrix/twin pairs of CaTiO3 have misorientation angles at 87°, 90° and 98°. The misorientations associated with the boundaries between twin/twin pairs formed by different twinning orientation relationships are noted at 90°, 91°, 92° and 98°. On the basis of the orientation relationships, the crystallography of cubic to orthorhombic and tetragonal to orthorhombic phase transformations in CaTiO3 is explored. The most favorable orientation relationships pertaining to such a phase transformation are ( 001 ) o [ 100 ] o || ( 03 1 ¯ ) c [ 3 ¯ 13 ] c between parent cubic and daughter orthorhombic phases and ( 001 ) o [ 100 ] o || ( 1 1 ¯ 2 ¯ ) t [ 8 ¯ 2 ¯ 3 ¯ ] t between parent tetragonal and daughter orthorhombic phases of CaTiO3.

Anisotropic field induced phase transitions and negative electrocaloric effect in rhombohedral Mn doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

The electrocaloric effect (ECE) of Mn doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT:Mn) single crystals with particular emphasis on the impact of crystallographic orientations and phase transitions were investigated systematically. Orientation-dependent phase transitions have been demonstrated by the dielectric and strain behaviors. Intriguingly, the negative ECE of –0.02 °C and –0.002 °C were obtained firstly in [001]-oriented PIN-PMN-PT:Mn crystals near the rhombohedral→tetragonal phase transformation and in [011]-oriented crystals near the rhombohedral→orthorhombic phase transformation, respectively. However, only the positive ECE was found in [111]-oriented crystals near the tetragonal→rhombohedral phase transition. Additionally, the maximum ECE temperature changes calculated in [001]-, [011]- and [111]-oriented crystals were 0.33 °C, 0.46 °C and 0.38 °C, respectively. Our results suggest that the negative ECE is attributed to electric field-induced phase transitions, whose critical field decreases with the increase of temperature. The phase transition-mediated coexistence of positive and negative effects in the relaxor-ferroelectric single crystals is beneficial to enhance the efficiency of the solid-state cooling devices.

Precursor-reforming protocol to 3D mesoporous g-C3N4 established by ultrathin self-doped nanosheets for superior hydrogen evolution

Graphitic carbon nitride (g-C3N4) has attracted enormous research attention as a promising low cost, visible-light driven semiconductor photocatalyst. However, low photoabsorption efficiencies and unsatisfactory charge separation limit the potential of g-C3N4 in many applications, motivating attempts to manipulate the structure and electronic properties of g-C3N4 to achieve improved performance. Here we describe a novel precursor-reforming strategy that ultimately affords 3D mesoporous ultrathin g-C3N4 with superior photocatalytic performance compared to conventional calcination-derived g-C3N4. We demonstrate that during hydrothermal treatment of melamine and urea, melamine undergoes an irreversible monoclinic to orthorhombic phase transformation, and the additive urea (excess typically 3-fold) serves as an additional N source and porogen. Calcination of the orthorhombic melamine yields mesoporous g-C3N4 with enhanced photoabsorption properties and an outstanding photoactivity. A 23-fold increased hydrogen evolution rate of 3579μmolh−1g−1 (λ > 420nm) was achieved with an apparent quantum efficiency (AQE) of 27.8% at 420 ± 15nm, a level of performance far beyond any AQE previously reported for ultrathin/porous/doped g-C3N4 photocatalyst. Our work conclusively demonstrates a new synthetic strategy towards high performance g-C3N4-based photocatalytic materials for energy applications.

Orthorhombic phase stabilization and transformation phase process in zirconia tantalum-doped powders and spark plasma sintering systems

The role of different amount (from 1 to 20 mol%) of tantalum Ta(V) into the zirconia lattice has been investigated in different powders systems prepared via co-precipitation and after calcination. The X-ray diffraction and Raman analyses, have confirmed the presence of an orthorhombic phase in all the samples. The stability of this phase has been investigated by “in situ” X-ray diffraction analysis from 100°C to 1000°C and after the subsequent cooling. A phase transformation mechanism, with the formation of a poor (monoclinic) and a rich phase (orthorhombic) in Ta has been consider in order to explain the XRD patterns obtained at different temperatures. The characterization of the orthorhombic phase on bulk ceramic specimens prepared via Spark Plasma Sintering (SPS) has been also investigated. SEM analysis has confirmed the presence of a two-phase system.