Stabilization Of Phase Research Articles

Demonstration of ferroelectricity in PLD grown HfO<sub>2</sub>-ZrO<sub>2</sub> nanolaminates

<abstract> <p>Ferroelectricity is demonstrated for the first time in Si(100)/SiO<sub>2</sub>/TiN/HfO<sub>2</sub>-ZrO<sub>2</sub>/TiN stack using pulsed laser deposition (PLD) and the effects of temperatures, partial oxygen pressures, and thickness for the stabilization of the ferroelectric phase were mapped. Thin films deposited at a higher temperature and a higher oxygen partial pressure have a higher thickness, demonstrating a better ferroelectric response with ~12 μC/cm<sup>2</sup> remnant polarization, a leakage current of 10<sup>−7</sup> A (at 8 V) and endurance > 10<sup>11</sup> cycles indicative of an orthorhombic crystal phase. In contrast, thin films deposited at lower temperatures and pressures does not exhibit ferroelectric behavior. These films can be attributed to having a dominant monoclinic phase, having lower grain size and increased leakage current. Finally, the effects of ZrO<sub>2</sub> as top and bottom layer were also investigated which showed that ZrO<sub>2</sub> as the top layer provided better mechanical confinement for stabilizing the orthorhombic phase instead of as the bottom layer.</p> </abstract>

Extraction Behavior of Lanthanoids(III) with Bis(2-ethylhexyl)phosphoric Acid into Ionic Liquid 1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide

The extraction behavior of 14 trivalent lanthanoids (Lns) with bis(2-ethylhexyl)phosphoric acid (HR) into a typical hydrophobic ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, was investigated. The extraction is so slow that a shaking time of more than 36 hours is needed to reach extraction equilibrium. Compared to the extraction system using toluene as an extraction solvent, the IL extraction system has higher extraction ability for all Lns and higher selectivity for some couples of Lns (e.g., Ce/La and Tb/Gd). The dependences of the distribution ratio on the aqueous pH and the HR concentration suggest that the main extracted species are neutral LnR3(HR)3 for light and middle Lns and Tb, but anionic LnR4(HR)2– and LnR5(HR)2– for heavy Lns (except for Tb). The addition of 1-octanol as a phase stabilizer decreases the extractability of Lns, which can be explained in terms of interaction between 1-octanol and HR dimer.

Comprehensive study on the origin of orthorhombic phase stabilization in Gd-doped HfO2 and DFT calculations.

In recent times, ultra-thin films of hafnium oxide (HfO2) have shown ferroelectricity (FE) attributed to the orthorhombic (o) phase of HfO2 with space group Pca21. This polar o-phase could be stabilized in the doped thin film of the oxide. In the present work, both polar and non-polar o-phases of HfO2 could be stabilized in Gd-doped bulk polycrystalline HfO2. Rietveld analysis of XRD data shows that the relative population of o-phases in the presence of the monoclinic (m) phase of HfO2 increases with increasing Gd-content. The local environment around the host atom has been investigated by time differential perturbed angular correlation (TDPAC) spectroscopy, synchrotron based X-ray near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements showed a reduction in grain size with increasing Gd-dopant indicating a solute drag effect. It could be established that the segregation of the Gd-dopant in the grain boundary is a thermodynamically favorable process and the solute drag effect plays an important role in nucleation of the o-phase in bulk HfO2. Stabilization of Gd in both Pbca and Pca21 phases of HfO2 was supported by defect formation energy calculations using density functional theory (DFT). The present study has important implications in future applications of HfO2 in ferroelectric devices and in understanding the role of dopants in stabilizing the o-phase of HfO2 in the bulk.

Parameters for ferroelectric phase stabilization of sputtered undoped hafnium oxide thin films

In this work, various stabilization factors for the ferroelectric phase of undoped hafnium oxide prepared by physical vapour deposition were investigated. The capping of the thin films with platinum top electrodes before annealing, as well as the amount of oxygen during sputter deposition and subsequent annealing was shown to have a significant influence on the resulting ferroelectric properties and phase of the HfO x layer. When the prepared films were not capped, only one specific set of process parameters was found to lead to the formation of the ferroelectric phase. We conclude that capping is a crucial condition for stabilizing the ferroelectric phase. Furthermore, it is shown that the amount of oxygen supply during all fabrication processes determines the resulting ferroelectric phase fraction for capped samples. Increasing the oxygen flow during sputtering and annealing results in a larger monoclinic phase fraction and thus a decrease of the remanent polarization.

Dielectric Switching and Ferroelectric Studies of α, γ PVDF Phases for Energy Storage Properties

This article presents the current–voltage (I–V) characteristics, ferroelectric (P–E) and energy density properties of polyvinylidene fluoride (PVDF) film samples synthesized by melt-press and solution-cast techniques. Our earlier work reported the α and γ -PVDF phase stabilization in PVDF film samples processed by melt-pressing and solution-casting respectively. In the present work, the I–V loops of pure PVDF film samples were recorded with variable delay time from 0.0005 to 1 s in order to understand the switching behavior response of molecular dipoles in different PVDF molecular conformations. The hysteresis behavior of I–V loops revealed the dominance of dipolar switching current in both the α and γ-PVDF phases. The slim P–E hysteresis loops with low remnant polarization Pr values ≈0.26 and 0.21 μC/cm2 at an applied electric field of 100 kV/cm for α and γ -PVDF phases respectively were traced. The dielectric energy storage efficiency η as calculated from P–E loop data was found to be ≈37.7% and 38.6%, respectively, for α and γ -phases of PVDF. The low leakage current and slim P–E hysteresis behavior in both the α and γ -phases of PVDF are favorable or desired for their application in dielectric energy storage capacitors.

Eu3+-activated SrY2O4:Ce4+/3+ red-phosphor for WLEDs: Structural and luminescent insights from experimental and theoretical approaches

Herein, single-phase Eu3+-activated SrY2O4:Ce4+/3+ red-emitting phosphor was produced by an adapted Pechini route under softer synthesis conditions (1100 °C in CO reducing atmosphere) compared to those reported so far. A detailed structural study conducted by Rietveld refinement and DFT calculations confirmed the presence of two hexa-coordinated Y3+ sites that are occupied by Eu3+. Cerium is present in a mixed oxidation state, where the proportion of Ce4+/Ce3+ was determined as 70/30% by X-ray photoelectron spectroscopy (XPS), and this influences the SrY2O4 phase stabilization by increasing the point defect concentration. A thorough analysis of the photoluminescent features of Eu3+-activated phosphor revealed its occupancy in at least two non-equivalent local sites belonging to the C1 point group. Furthermore, the excited state dynamics of the phosphors were enlightened by the theoretical band structure determination. Finally, 3%-doped sample exhibited the highest intrinsic quantum yield (81%), which qualifies these materials to be used as red-emitting components for solid-state lighting.

Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni49Mn32Ga19 Ferromagnetic Shape Memory Ribbons

In our work, the kinetics of martensitic transformations and the influence of thermal treatments on martensitic transformations, as well as the related magnetic properties of the Ni49Mn32Ga19 ferromagnetic shape memory melt-spun ribbons, have been investigated. Thermal treatments at 673 K for 1, 4 and 8 h can be considered an instrument for fine-tuning the performance parameters of alloys. One-hour thermal treatments promote an improvement in the crystallinity of these otherwise highly textured ribbons, reducing internal defects and stress induced by the melt-spinning technique. Longer thermal treatments induce an important magnetization rise concomitantly with a slight and continuous increase in martensitic temperatures and transformation enthalpy. The activation energy, evaluated from differential scanning calorimeter experimental data with a Friedman model, significantly increases after thermal treatments as a result of the multi-phase coexistence and stabilization of the non-modulated martensitic phase, which increases the reverse martensitic transformation hindrance.

Shrinkage features, microstructure evolution and properties of Gd2O3-MgO optical composite ceramics with Zr as phase stabilizer

A novel composite ceramic, composed of equal-volumetric Zr-stabilized Gd2O3 and MgO phases, was prepared to be transparent in mid-wave infrared range. Zr stabilized Gd2O3 is proved to have a lower lattice parameter (10.7516 Å) using XRD refinement. Pressureless sintering behavior of Gd2O3-MgO with/without 2 at% Zr-doping (naming ZGM and GM) was studied via the real-time observation technique. The shrinkage of ZGM green body proceeds steadily up to 1400 °C while that of the undoped one shrinks sharply at 1250 °C due to Gd2O3 phase transition. The segregation of Zr element along the grain boundaries of Zr-Gd2O3 creates a synergized effect on the grain refinement with pinning effect. Dense ZGM ceramics exhibit superior transmittance of 78.3 %‐85.6 % at 3–5 µm, which show good consistency with the calculated values. The refractive index of Zr- Gd2O3 varies from 1.87 at 3 µm to 1.80 at 5 µm, which is smaller than those of monoclinic Gd2O3.

Measurement-device-independent quantum key distribution with passive time-dependent source side channels

While measurement-device-independent (MDI) quantum key distribution (QKD) allows two trusted parties to establish a shared secret key from a distance without needing to trust a central detection node, their quantum sources must be well characterized, with side channels at the source posing the greatest loophole to the protocol's security. In this paper, we identify a time-dependent side channel in a common polarization-based QKD source that employs a Faraday mirror for phase stabilization. We apply a recently developed numerical proof technique [Phys. Rev. A 99, 062332 (2019)] to quantify the sensitivity of the secret key rate to the quantum optical model for the side channel, and to develop strategies to mitigate the information leakage. In particular, we find that the MDI three-state and BB84 protocols, while yielding the same key rate under ideal conditions, have diverging results in the presence of a side channel, with BB84 proving more advantageous. While we consider only a representative case example, we expect the strategies developed and key rate analysis method to be broadly applicable to other leaky sources.

A Thermodynamic Study on the Interaction between RH-23 Peptide and DMPC-Based Biomembrane Models.

Investigation of the interaction between drugs and biomembrane models, as a strategy to study and eventually improve drug/substrate interactions, is a crucial factor in preliminary screening. Synthesized peptides represent a source of potential anticancer and theragnostic drugs. In this study, we investigated the interaction of a novel synthesized peptide, called RH-23, with a simplified dimyristoylphosphatidylcholine (DMPC) model of the cellular membrane. The interaction of RH-23 with DMPC, organized either in multilamellar vesicles (MLVs) and in Langmuir-Blodgett (LB) monolayers, was assessed using thermodynamic techniques, namely differential scanning calorimetry (DSC) and LB. The calorimetric evaluations showed that RH-23 inserted into MLVs, causing a stabilization of the phospholipid gel phase that increased with the molar fraction of RH-23. Interplay with LB monolayers revealed that RH-23 interacted with DMPC molecules. This work represents the first experimental thermodynamic study on the interaction between RH-23 and a simplified model of the lipid membrane, thus providing a basis for further evaluations of the effect of RH-23 on biological membranes and its therapeutic/diagnostic potential.

The Influence of Potassium Salts Phase Stabilizers and Binder Matrix on the Properties of Novel Composite Rocket Propellants Based on Ammonium Nitrate.

The environmental impact and availability of ingredients are vital for the new generation of rocket propellants. In this context, several novel composite propellants were prepared based on the "greener" oxidizer phase-stabilized ammonium nitrate (PSAN), a micronized aluminum-magnesium alloy fuel, iron oxide powder burn rate modifier, triethylene glycol dinitrate (TEGDN) energetic plasticizer and a polyurethane (PU) binder. The novelty of this study is brought by the innovative procedure of synthesizing and combining the constituents of these heterogeneous compositions to obtain high-performance "eco-friendly" rocket propellants. The polymorphism shortcomings brought by ammonium nitrate in these energetic formulations have been solved by its co-crystallization with potassium salts (potassium nitrate, potassium chromate, potassium dichromate, potassium sulphate, potassium chlorate and potassium perchlorate). Polyester-polyol blends, resulting from recycled post-consumer polyethylene terephthalate (PET) glycolysis, were utilized for the synthesis of the polyurethane binder, especially designed for this type of application. To adjust the energetic output and tailor the mechanical properties of the propellant, the energetic plasticizer TEGDN was also involved. The performance and safety characteristics of the novel composites were evaluated through various analytical techniques (TGA, DTA, XRD) and specific tests (rate of combustion, heat of combustion, specific volume, chemical stability, sensitivity to thermal, impact and friction stimuli), according to NATO standards, providing promising preliminary results for further ballistics investigations.

Stabilization of the (C2H5)4NHSO4 High-Temperature Phase in New Silica-Based Nanocomposite Systems.

In this study, the electrotransport, thermal and structural properties of composite solid electrolytes based on (C2H5)4NHSO4 plastic phase and silica (1 - x)Et4NHSO4-xSiO2, where x = 0.3-0.9) were investigated for the first time. The composites were prepared by mechanical mixing of silica (300 m2/g, Rpore = 70Å) and salt with subsequent heating at temperatures near the Et4NHSO4 melting point. Heterogeneous doping is shown to change markedly the thermodynamic and structural parameters of the salt. It is important that, with an increase in the proportion of silica in the composites, the high-temperature disordered I41/acd phase is stabilized at room temperature, as this determines the properties of the system. Et4NHSO4 amorphization was also observed in the nanocomposites, with an increase in the matrix contents. The enthalpies of the endoeffects of salt melting and phase transitions (160 °C) changed more significantly than the Et4NHSO4 contents in the composites and completely disappeared at x = 0.9. The dependence of proton conductivity on the mole fraction reached a maximum at x = 0.8, which was three or four orders of magnitude higher than the value for pure Et4NHSO4, depending on the composition and the temperature. The maximum conductivity values were close to those for complete pore filling. The conductivity of the 0.2Et4NHSO4-0.8SiO2 composite reached 7 ∗ 10-3 S/cm at 220 °C and 10-4 S/cm at 110 °C.

Retention Improvement of HZO-Based Ferroelectric Capacitors with TiO2 Insets.

The influence of the bottom TiO2 interfacial layer grown by atomic layer deposition on the ferroelectric properties of the TiN/Hf0.5Zr0.5O2/TiN capacitors is systematically investigated. We show that the integration of the TiO2 layer leads to an increase in the polar orthorhombic phase content in the Hf0.5Zr0.5O2 film. In addition, the crystalline structure of the Hf0.5Zr0.5O2 film is highly dependent on the thickness of the TiO2 inset, with monoclinic phase stabilization after the increase of TiO2 thickness. Special attention in this work is given to the key reliability parameters-retention and endurance. We demonstrate that the integration of the TiO2 inset induces valuable retention improvement. Using a novel approach to the depolarization measurements, we show that the depolarization contribution to the retention loss is insignificant, which leaves the imprint effect as the root of the retention loss in TiN/TiO2/Hf0.5Zr0.5O2/TiN devices. We believe that the integration of the insulator interfacial layer suppresses the scavenging effect from the bottom TiN electrode, leading to a decrease in the oxygen vacancy content in the Hf0.5Zr0.5O2 film, which is the main reason for imprint mitigation. At the same time, although the observed retention improvement is very promising for the upcoming technological integration, the field cycling testing revealed the endurance limitations linked to the phase transitions in the TiO2 layer and the rise of the effective electric field applied to the Hf0.5Zr0.5O2 film.

Structural and charge carrier dynamics study of Dy stabilized La6MoO12 ionic conductors

Room temperature single phase stabilization of different metals (Zr, Cd, and Ca) doped La6MoO12 compound was achieved by incorporating Dy2O3 using the solution combustion method. Rietveld refined X-ray diffraction profiles showed cubic fluorite (Fm3¯m) structure for all the compositions. The optical bandgap, calculated from ultraviolet-visible spectra, exhibited blue shifts with decreasing dopant ionic radius. The photoluminescence spectra confirmed the charge carrier's various trapping or defect states. The complex impedance plot exhibited non-Debye-type relaxation with a negative temperature coefficient of resistance (NTCR). It also indicated that the dopant might act as an acceptor or donor depending upon its valency. The ac conductivity was found to follow the small polaron hopping mechanism. A thermally activated single relaxation process was observed. The composition La5.4Dy0.4Zr0.2MoO12.1 showed the highest conductivity, 1.05 × 10−4 Ω−1 cm−1 at 680 °C. The scaling of spectra indicated temperature and composition independent charge carrier mechanism.

Effect of ratios of dopant contents on the electrical conductivity of Bi2O3 ceramics co–doped with some rare earth oxides

In this study, Bi 2 O 3 –based ceramic powders co–doped with differing quantities of Dy 2 O 3 , Sm 2 O 3 , Ho 2 O 3 , and CeO 2 rare earth oxides have been synthesized using the solid state reactions under atmospheric conditions. The XRD patterns revealed that the Dy–rich samples were more effective in stabilizing the cubic δ–phase than the others. The DTA curve of sample S1 (5%Dy: 5%Sm: 5%Ho: 5%Ce) had an endothermic peak at approximately 730 °C, indicating a phase transition from monoclinic α–phase to cubic δ–phase. The conductivity measurements show that sample S11 (10%Dy: 5%Sm: 5%Ho: 5%Ce) had the highest electrical conductivity among cubic δ–phase stabilized samples with 0.027 S/cm at 700 °C. The dopant content ratios, as well as concentration, had a significant impact on electrical conductivity and phase stabilization. According to the SEM images, the grain sizes were not uniform across the surface and decreased as the dopant concentration increased. The EDX pattern of sample S1 verified the presence of all elements in compositions with different peak locations on the pattern and the absence of any peaks indicating impurities. Order-disorder transition (ODT), which is a structural arrangement in the anion sublattice, occurred at approximately 600 °C in Ce-rich samples, according to conductivity plots produced as a function of temperature. • The concentration and type of dopant are critical in stabilizing the high ion conductor cubic δ–phase. • The DTA curve of the sample produced with the lowest concentration of dopant reveals a phase transition from the α–phase to the δ–phase at around 730 °C due to the presence of an endothermic peak on its thermal curve. • The order-disorder transition (ODT), which signifies a structural arrangement of anions in the oxygen sublattice, is only evident in Ce-rich samples. • The FE–SEM images indicate that as the dopant concentrations increase, the porosity along on the surface also begins to rise and the grain boundary line undergoes a significant change.

Molecular and biochemical approach for understanding the transition of amorphous to crystalline calcium phosphate deposits in human teeth.

Calcium phosphate (CaP) deposition during bone mineralization starts with the aggregation of Posner's clusters Ca9(PO4)6 into amorphous Ca-phosphate (ACP), which then transforms into crystalline CaP and finally maturates to hydroxyapatite (HA). Using dentin/enamel of human teeth as a model system, we show that the physiological inorganic polymer polyphosphate (polyP), a phosphate donor in mineralization, prevents the transition from amorphous to crystalline CaP at concentrations>15wt%. Stabilization of the amorphous phase of CaP by polyP is reversed by hydrolysis of the polymer by alkaline phosphatase (ALP), an enzyme that releases phosphate for mineralization. It is still present in calcified enamel and dentin, as shown here by immunostaining and enzyme activity measurements. The phase transfer into crystalline CaP can be prevented by the ALP inhibitor levamisole. Besides TEM and SEM, the modulating effects of polyP and ALP on the kinetics of the phase transition from amorphous to crystalline CaP are demonstrated and confirmed by XRD and FTIR analyses. Molecular modeling studies show that the polyP chains, due to their dimensions, are able to penetrate into the channels between the Posner molecules, preventing cluster association to ACP and impairing HA crystal formation.

Stabilization of the ferroelectric phase of potassium nitrate in a (KNO3)0,9(NaNO2)0,1 double salt system

The temperature dependences of the dielectric constant, the third harmonic coefficient and the DTA signal of the (KNO3)0.9/(NaNO2)0.1 double salt system in comparison with pure potassium nitrate have been investigated. The studies were carried out in the temperature range 300–455 K. The expansion of the temperature range of the existence of the potassium nitrate ferroelectric phase in (KNO3)0.9/(NaNO2)0.1 was found. It is shown that the ferroelectric phase of potassium nitrate in (KNO3)0.9/(NaNO2)0.1 can occur not only upon cooling, but also upon heating.

Complex Additive‐Assisted Crystal Growth and Phase Stabilization of α‐FAPbI3 Film for Highly Efficient, Air‐Stable Perovskite Photovoltaics

AbstractSolution‐processed formamidinium lead iodide (FAPbI3) perovskite is entropically metastable, and it exhibits condition‐induced crystal polymorphism. Under an ambient atmosphere, the photoactive black α‐FAPbI3 converts easily to photoinactive yellow δ‐FAPbI3. This α → δ phase degradation is further accelerated upon exposure to high temperature/humidity, directly threatening the performance and stability of perovskite solar cells (PSCs). Herein, cesium iodide‐lead iodide:dimethyl sulfoxide (CsI‐PbI2:DMSO) complex is introduced as a phase stabilizer to modulate the crystallization of α‐FAPbI3 perovskite from δ‐FAPbI3 precursor and simultaneously, serve as a defect passivator to suppress trap states formation. Theoretical simulations and experimental results reveal the pivotal role of complex additive in optimizing the energy band alignment and optoelectronic properties of α‐FAPbI3 perovskite and most importantly, hindering the α → δ phase transition. The best PSC device based on the additive‐engineered perovskite film achieves an efficiency of ≈21.9%, which is ≈11% higher than that of its pristine counterpart (≈19.8%). In addition, the incorporation of CsI‐PbI2:DMSO complex remarkably enhances the long‐term stability and photostability of the PSCs by inhibiting ion migrations and preserving the α‐phase in FAPbI3 perovskite. The additive engineering presented herein offers a route to produce FAPbI3‐based PSCs with improved performance, stability, and reproducibility.

Alkylation for removing trace olefins from reforming aromatics over novel Al2O3@SO42-/ZrO2 catalysts derived from the ZrO2-coated γ-Al2O3 strategy

Sulfated zirconia, as a promising catalyst in various acid-catalytic reactions, still suffer from unsatisfactory catalytic stability and regeneration performance due to severe leaching of sulfur species, while aluminum modification can effectively overcome these drawbacks. Unfortunately, the limited acceptability of aluminum content by co-precipitation and milling methods remains a critical issue. Herein, an effective strategy of coating sulfated zirconia on the surface of γ-Al2O3 was developed to synthesize the novel Al2O3@SO42-/ZrO2 catalyst with high aluminum content. The synthesis variables were investigated and systematically optimized. The structural and acidic properties of Al2O3@SO42-/ZrO2 were determined by XRD, HR-TEM equipped with EDX, N2 adsorption-desorption isotherms, EA, FT-IR, NH3-TPD and Py-FTIR. Results indicated that the unique structure constructed by sulfated zirconia coated on γ-Al2O3 not only realized the stabilization of favorable tetragonal zirconia phase even at exceedingly high aluminum content but also promoted Brønsted acid sites. Accordingly, the optimal Al2O3@SO42-/ZrO2-50% performed outstanding catalytic activity and stability, given the olefins conversion of 98%-75% during the continuous reaction experiment. Owing to the alleviation of sulfur loss by Al-promoting effects, excellent regeneration performance, with olefins conversion only slightly declining after 4 consecutive reaction-regeneration cycles, was also obtained. The mechanistic pathway for the alkylation of olefins with aromatics over Al2O3@SO42-/ZrO2 was also investigated and proposed by GC–MS analysis.

Exploratory phase stabilization in heteroepitaxial gallium oxide films by pulsed laser deposition

Gallium oxide (Ga2O3) is featured by various types of polymorphs that exhibit distinct properties for a broad range of applications. Selective stabilization of distinct Ga2O3 polymorphs is highly desired, but is usually limited by impurity phase formation. Here we report the controlled growth of metastable gallium oxide films by pulsed laser deposition (PLD), and explore a comprehensive phase evolution picture tuned by key synthesis parameters, substrate orientations, and extrinsic tin (Sn) dopants. We demonstrate the stabilization of both undoped and Sn-doped α-Ga2O3 films by selecting a-plane sapphire substrates, and find that Sn dopants can largely broaden the growth window of α-Ga2O3. Besides, Sn-doped ε-Ga2O3 is more favored than β-Ga2O3 to be stabilized on c-plane substrates, and the oxygen pressure is the critical factor to dictate the ε-Ga2O3 formation. The structural impact on the thermal transport among these metastable Ga2O3 films is investigated, which shows a maximum value of 5.66 Wm−1K−1 in α-Ga2O3 and a minimum value of 1.04 Wm−1K−1 in amorphous Ga2O3. The native defects of these phases are sensitive to the Sn doping, which exhibits distinct response for deep ultraviolet photodetection. This study establishes a synthesis guideline of metastable Ga2O3 polymorphs by PLD and provides insights into selective phase stabilization of transition metal oxides with various crystal phases.