Polymorphic Phase Transformation Research Articles

Temperature-dependent synchrotron XRD study and electrical properties of the (1-x)BZT-(x)BCT lead-free piezoceramics

In recent years, researchers have shown the feasibility of the BZT-xBCT lead-free piezoelectric ceramics for using in various applications such as actuator, energy harvester, high-frequency ultrasonic transducer, etc. However, little evidence of temperature-dependent electrical properties of the BZT-xBCT ceramic was found. Moreover, some researchers have utilized Raman spectroscopy to observe the phase transition of the BZT-xBCT ceramic, but the Raman spectra of ferroelectric polymorphic phases are almost identical and hard to distinguish. In contrast, synchrotron radiation exhibits a high degree of monochromatization and collimation with smaller wavelength than x-ray tubes, resulting in the improvement of resolution for identifying the overlapping peaks. Therefore, this work aims to determine phase coexistence of the BZT-xBCT ceramic near phase boundary region by using high-resolution synchrotron x-ray powder diffraction in comparison with the temperature-dependent electrical properties. This work found that the occurrence of thermally-induced polymorphic phase transformations for the BZT-xBCT ceramics plays a significant role in the observed temperature-dependent electrical properties. Moreover, this work observed a trace of surface damaged layer (the presence of low-angle shoulder in the synchrotron XRD profiles) from mechanical grinding during sample preparation for XRD measurement, which has not previously been found in the BZT-xBCT ceramics. These finding will help to better understand the temperature-dependent functional properties of the BZT-xBCT ceramic for transferring into practical applications.

Nucleation control and separation of ethyl maltol polymorphs under different growth conditions through solution crystallization process in selected solvent environments

Nucleation control, separation and growth of Form-I, II & III polymorphs of ethyl maltol were achieved through solution crystallization processes. Morphology, unit cell structure and polymorphic phase transformations were revealed for the first time.

Effect of organic acids on the solid-state polymorphic phase transformation of piracetam

Metastable polymorphs are frequently used in oral solid dosage forms to enhance the absorption of poorly water-soluble drug compounds. However, the solid phase transformation from the metastable polymorph to the thermodynamically stable polymorph during manufacturing or storage poses a major challenge for product development and quality control. Here, we report that low-content organic acids can exhibit distinct effects on the solid-state polymorphic phase transformation of piracetam (PCM), a nootropic drug used for memory enhancement. The addition of 1 mol% citric acid (CA) and tricarballylic acid (TA) can significantly inhibit the phase transformation of PCM Form I to Form II, while glutaric acid (GA) and adipic acid (AA) produce a minor effect. A molecular simulation shows that organic acid molecules can adsorb on the crystal surface of PCM Form I, thus slowing the movement of molecules from the metastable form to the stable form. Our study provides deeper insights into the mechanisms of solid-state polymorphic phase transformation of drugs in the presence of additives and facilitates opportunities for controlling the stability of metastable pharmaceuticals.

Developing fired clay bricks by incorporating scrap incinerated waste and river dredged sediment

The global extraction of several billions of clean clay resources, which destroy millions square meters of land, is triggering environmental problems. Incorporating different dosages of incinerated waste or dredged sediment in bricks production has been studied by many researchers. Research articulating the combined effect of incinerated waste material (IWM) and river dredged sediments (RDS) addition on the performance of bricks is scarce. This paper aims to present findings on the engineering performance of fired bricks developed with the addition of IWM and RDS. In this regard, bricks were made with 5 wt% IWM and different dosages of RDS (i.e., 0 – 15 wt%). Physical, durability, mechanical, thermal and microstructure of the developed bricks is examined. Bricks’ shrinkages were found meeting quality performance criterion in the 1.42 – 4.11% range. The highest bulk density of 1.85 g/cm3 permit to classify bricks obtained as lightweight. Water absorptions were mostly within the acceptable 20% tolerance level postulating the developed bricks high durability standard. Compressive strength reductions, which were confined within 5.28 and 21.57 MPa, showed the developed bricks applicability to structural weight-supporting construction as well as specialized engineering construction works. The 40.5% thermal conductivity reduction in WB15 bricks (at 800 °C) theorized its suitability for thermal insulation construction. Mineralogical and morphological analyses of fired bricks clearly showed kaolinite polymorphic phase transformation, which contributed to the different morphologies in the brick matrices. Consequently, reuse of IWM and RDS offered a chance to advance sustainable use of scarce clay resources in lightweight and thermal insulation brick production.

In situ investigation of the ferroelectric phase transition in improper ferroelectric YMnO3 thin films by electron energy loss spectroscopy

The crystal and electronic structure of $\mathrm{YMn}{\mathrm{O}}_{3}$ thin films at the paraelectric-ferroelectric phase transition are monitored by scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) during in situ heating experiments. At the phase transition of a 14-unit-cell-thick film at $\ensuremath{\sim}325\phantom{\rule{0.16em}{0ex}}{}^{\ensuremath{\circ}}\mathrm{C}$, we observe a clear transition from the polar $P{6}_{3}cm$ to the centrosymmetric $P{6}_{3}/mmc$ space group, manifested by the disappearance of the unit-cell tripling. Further, we reveal significant changes in the EELS data across the phase transition, and interpret them with the help of real-space multiple-scattering calculations. Upon crossing the Curie temperature, striking changes in the O-$K$ near-edge structure are identified, which are attributed to a modification in the Y $4d--\mathrm{O} 2p$ hybridization. In particular, a weakening of the Y $4d{}_{z}{}^{2}--\mathrm{O} 2{p}_{z}$ hybridization is detected for the paraelectric phase compared to the ferroelectric phase. Upon cooling below the Curie temperature, the ferroelectric phase is recovered and a stronger hybridization along the $c$-axis polarization direction is restored, stabilizing the zone-boundary ${\mathrm{K}}_{3}$ phonon mode. Our findings demonstrate the high sensitivity of the O-$K$ near-edge structure to structural distortions in $\mathrm{YMn}{\mathrm{O}}_{3}$ polymorphs and lay the groundwork for future studies on polymorphic phase transformations in improper ferroelectrics whose ferroelectricity emerges through coupling to a nonpolar lattice distortion.

On polyamorphism in heterophase matter

Structural and thermodynamic features of continuous and discontinuous polymorphic phase transformations in amorphous matter caused by the rearrangement of mesoscopic molecular associations are considered. Polyamorphism of fluids expanded mercury, and the orientationally-disordered fullerite C60, pure and doped by heavy rare gases, is summarized.

Contrasting magnetic properties of polymorphic TbPt3

In this work, we report the contrasting magnetic behaviour of a bimorphic intermetallic compound TbPt 3 that undergoes a structural phase transformation from cubic AuBe 5 -type structure to the cubic AuCu 3 -type structure on annealing at high temperature for a very short time. The magnetic ground state configuration of TbPt 3 changes from ferromagnetic (FM) in AuBe 5 -type crystalline phase to antiferromagnetic (AFM) in AuCu 3 -type phase. However, the AFM ground state of the AuCu 3 -type compound is unstable, as a moderate magnetic field can induce the FM character through metamagnetic transformation. To understand the said crystallographic as well as magnetic transformations, structural and magnetic ab-initio calculations have been carried out for both phases. From theoretical calculations we have proposed that although the AuBe 5 -type structure of TbPt 3 irreversibly transforms to the AuCu 3 -type TbPt 3 by a very short heat treatment, the application of moderate magnetic field on AuCu 3 -type structure may result in recovering the magnetic properties of AuBe 5 -type structure of TbPt 3 . As the two different polymorphs exist simultaneously at ambient condition, TbPt 3 thus provides us a great opportunity to study directly the effect of crystal structure on its physical properties and vice versa. • TbPt 3 compound shows polymorphic structural phase transformation on annealing at high temperature. • Ground state magnetic configurations of TbPt 3 changes from FM to AFM under structural transformation. • Antiferromagnetic TbPt 3 compound exhibits field induced metamagnetic transition to ferromagnetism.

STUDY OF PHASE FORMATION PROCESSES IN CER-CER TYPE INERT MATRICES BASED ON OXIDE COMPOUNDS

The purpose of this work is to study the processes of phase formation in the samples (1-x)ZrO2 – xAl2O3 ceramics depending on the variation of the oxide components, as well as to establish changes in the structural parameters and degree of crystallinity. The choice of zirconium and aluminum oxides as the basis for cer-cer inert matrices for nuclear fuel is due to their physical, chemical, structural and mechanical properties, the combination of which will produce a new type of ceramics with great potential in the field of nuclear fuel. These oxide compounds have high thermal stability and resistance to high temperatures, which also allows their use as a basis for disperse nuclear fuel for new-generation hightemperature nuclear reactors. The method of mechanochemical milling followed by thermal annealing was chosen to obtain ceramics based on oxide compounds. The choice of grinding conditions, as well as the subsequent thermal annealing was chosen to initiate the processes of phase transformations and structural changes as a result of thermal influence and partial relaxation of the deformation distortions and metastable formations initiated during grinding. The X-ray diffraction method was chosen as the main method to study the processes of phase transformation and structural changes. During the studies it was found that the addition of aluminum oxide leads to the structural ordering of the main monocline phase ZrO2, as well as the formation of solid solutions of substitution and introduction. At equal concentrations of the oxide components using the method of X-ray phase analysis was established polymorphic phase transformation in zirconium dioxide, the presence of which indicates the processes of phase transformation arising from the addition of zirconium oxide and changes in the phase formation processes.

Quantitative Monitoring of Cocrystal Polymorphisms in Model Tablets Using Transmission Low-Frequency Raman Spectroscopy

Cocrystallization is a technique for improving the physical properties of active pharmaceutical ingredients. However, cocrystals can transform into more stable polymorphs as well as dissociate to original materials. Therefore, an analytical technique is required to determine the polymorphic transformation quickly and accurately in tablets. The purpose of this study is to develop a method to monitor cocrystal polymorphs in model tablets using transmission low-frequency Raman spectroscopy. The tablets, consisting of only metastable polymorphs of caffeine-glutaric acid cocrystals, were stored under various relative humidity levels. The composition of the cocrystal polymorphs were calculated from a calibration curve relating the actual composition to the predicted values calculated by partial least squares regression processing of low-frequency Raman spectra. The metastable form gradually converted to a stable form, and polymorphic phase transformation occurred with increasing relative humidity. Ninety-six percent of the metastable form converted into a stable form stored at 25 °C after 3 h at 95% RH. In conclusion, transmission low-frequency Raman spectroscopy can be used to quantitatively monitor cocrystal polymorphs. This technique is one of the candidate techniques to quantifiably evaluate the physico-chemical stability of cocrystal polymorphs in tablets.

Oxidation mechanism of a near β-Ti alloy

Near β-Ti alloys, a perfect candidate material for numerous applications in the aerospace, are expected to exhibit high temperature endurability. Here, in order to evaluate the high temperature oxidation mechanism of the near β-Ti alloy, detailed microstructural characterization was performed on a near β-Ti alloy, Ti-55511 alloy after isothermal heat treatment at 600 °C in a tube furnace. Parabolic oxidation kinetics was observed. The oxide layer consisted of Al2O3, TiO2, VO2, and Magnéli phases. Polymorphic phase transformations and Magnéli phases played critical roles in the oxide layer thickening. The formation of defects was highly correlated with the incorporation of oxygen into Al2O3 and VO2, which resulted in lattice distortion of the oxides. Continuous oxidation led to the formation of the higher-valence oxide V2O5 in VO2 particles.

Investigation of Glycine Polymorphic Transformation by In Situ ATR-FTIR and FT-Raman Spectroscopy

The solution-mediated phase transformation of α-form to γ-form glycine, including dissolution of metastable α-form, nucleation, and growth of stable γ-form during polymorphic transformation, was investigated using in situ attenuated total-reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and Fourier transform Raman spectroscopy (FT-Raman). The mechanistic influence of operating parameters such as agitation speed, crystallization temperature, α-form seed concentration, and NaCl concentration on polymorphic phase transformation was examined. When the agitation speed, crystallization temperature, and NaCl concentration were increased, the polymorphic transformation process was improved due to the promotion of nucleation and growth of stable γ-form, in addition to the promotion of dissolution of metastable α-form. Moreover, the time to induce γ-form nucleation and complete conversion of α-form to γ-form was also reduced with increasing α-form seed concentration.

In situ discrimination of polymorphs and phase transformation of sulfamerazine using quartz crystal microbalance

A novel strategy utilizing the quartz crystal microbalance (QCM) was developed for the in situ discrimination of polymorphic nucleation (form-I and form-II) and phase transformation of sulfamerazine (SMZ) in cooling crystallization. According to Ostwald's rule of stages, metastable form-I of SMZ is first nucleated and then shifted to stable form-II by solution-mediated phase transformation. Through surface modification with the self-assembled monolayer technique of a functional group, QCM distinctively detects the formation of the two polymorphs. The results indicated that –NH2 (among the several functional groups tested) selectively accommodated stable form-II on the QCM sensor's surface and completely prevented the adsorption of metastable form-I on the surface. Therefore, the–NH2-terminated QCM detected the formation of form-I only using the solution viscosity variation on the surface. However, it monitored the nucleation and growth of form-II via the solid mass change on the surface during the phase transformation of form-I to form-II. This strategy suggests a new and precise solution for in situ discrimination of SMZ polymorphs and their phase transformation.

Polymorphic Phase Transformations in Crystalline Solid Dispersions: The Combined Effect of Pressure and Temperature

Polymorphic Phase Transformations in Crystalline Solid Dispersions: The Combined Effect of Pressure and Temperature

Isolation and Stabilization of the Metastable Form‐II Polymorph of Vanillin

AbstractIsolation and stabilization of the rare metastable polymorphic form‐II of vanillin was achieved by employing the template‐enhanced crystallization method through heterogeneous nucleation induced with Cu wire as the template surface. Irrespective of supersaturation, the solution induces the nucleation of the fine needle‐like form‐II polymorph on the surfaces of the Cu wire within a shorter induction period. This method has two main advantages: (i) It induces the nucleation of only the metastable form‐II polymorph of vanillin and (ii) stabilizes its steady growth without showing any solution‐mediated polymorphic phase transformation throughout. Thus, the harvested form‐II crystals stay for longer periods without showing any phase transformation at ambient conditions, with maximum stability.

Effect of Taylor vortex wavelength on polymorphic crystallization of L-histidine

Axial wavelength is a key characteristic parameter of Taylor vortex flows. Thus, in the current study, the effect of Taylor vortex wavelength on the polymorphic nucleation and phase transformation of L-histidine was examined. The vortex wavelength was altered by altering the gap width between the outer and inner cylinders. Further, the vortex velocity was changed by controlling the inner cylinder rotation speed. Owing to the promotion of stable nucleation by the periodic fluid motion, the primary polymorphic fraction of the stable Form A of L-histidine in Taylor vortex flow [Couette–Taylor (CT) crystallizer] was much greater than that in a turbulent eddy flow [mixing tank (MT) crystallizer]. As the vortex wavelength decreased, stable nucleation was promoted, thus increasing the initial polymorphic fraction of the stable Form A. Moreover, the initial polymorphic fraction of the stable Form A increased as the vortex velocity increased. These experimental results are described based on molecular alignment effect of Taylor vortex on stable nucleation. The phase transformation of L-histidine was also strongly influenced by the vortex wavelength and vortex velocity. Hence, the rate of phase transformation in CT crystallizer was approximately ten-fold better than MT crystallizer.

Mixture of CaCO 3 Polymorphs Serves as Best Adsorbent of Heavy Metals in Quadruple System

This study compares and analyzes removal of Pb (II), Cu (II), Mn (II), and Zn (II) from aqueous solution as individual ions (monometal system) or as mixed ions (quadruple system) by commercial laboratory-grade calcium carbonate (C–CaCO3) and as-synthesized CaCO3 (S–CaCO3) as adsorbents. This was performed to determine whether heavy metal ion adsorption can be influenced by the polymorphic phases of CaCO3. C–CaCO3 and S–CaCO3 were equally efficient in the removal of Pb (II) and Cu (II) from a monometal system. However, S–CaCO3 exhibited only 49.3% ± 0.14 heavy metal removal when compared with 96.7% ± 0.08 by C–CaCO3 in a quadruple system. FTIR and HR-SEM analysis revealed C–CaCO3 consisted of a mixture of calcite and aragonite polymorphs, whereas S–CaCO3 was pure calcite polymorph. These results indicated the importance of identification of the polymorphic phase and phase transformation in any experiment while utilizing CaCO3 as adsorbent.

Transforming polymorphs, melting, and boiling during cookoff of PETN

Transforming polymorphs, melting, and boiling are physical processes that can accelerate decomposition rates during cookoff of PETN and make measurements difficult. For example, splashing liquids from large bubbles filled with decomposition products clog pressure tubing in sealed experiments. Boil over can also extinguish thermal excursions in vented experiments making ignition difficult. For better measurements, we have modified the Sandia Instrumented Thermal Ignition (SITI) experiment to obtain better sealed and vented cookoff data for PETN by reducing the sample size and including additional gas space to prevent clogged tubing and boil over. Ignition times were not affected by 1) increasing the gas space by a factor of 3 in sealed SITI experiments or by 2) venting the decomposition gasses. That is, thermal ignition of PETN is not pressure dependent and the rate-limiting step during PETN decomposition likely occurs in the condensed phase. A simple decomposition model was calibrated using these observations and includes rate acceleration caused by melting and boiling. The model is used to predict internal temperatures, pressurization, and thermal ignition in a wide variety of experiments. The model is also used with SITI data to estimate the previously unreported latent enthalpy (5 J/g) associated with the α (PETN-I) to β (PETN-II) polymorphic phase transformation of PETN.

Study on Structure, Stability, and Phase Transformation of Dufulin Polymorphs

Study on Structure, Stability, and Phase Transformation of Dufulin Polymorphs

Hybrid ZnSe‐SnSe2 Nanoparticles Embedded in N‐doped Carbon Nanocube Heterostructures with Enhanced and Ultra‐stable Lithium‐Storage Performance

AbstractBimetallic selenide composites with multiple valence transitions and high theoretical capacities have attracted great attention as lithium‐ion‐battery anodes, but their rapid capacity fading and scarce research limit their development. Herein, novel hybrid ZnSe‐SnSe2 nanoparticles embedded in N‐doped carbon nanocubes (ZSS⊂NCNs) are synthesized by a facile nucleation assembly, carbon coating, and in situ selenation route. The obtained uniform ZSS⊂NCN materials exhibit high surface area, N‐doping carbon shell, extra inner void space, and excellent resilient mechanism nanostructure, which provide amounts of active sites, outstanding electrochemical kinetics, and buffer the volume expansion in the conversion and alloy/dealloy processes. For lithium‐ion‐battery half‐cells, the uniform ZSS⊂NCN materials display a high initial coulombic efficiency of 81.9 %, an increased capacity of 846.6 mA h g−1 at 0.2 A g−1 after 100 cycles, and an excellent rate capability (414.1 mA h g−1 at 5 A g−1). When assembled with a LiMn2O4 cathode, the ZSS⊂NCNs//LiMn2O4 full cells also present excellent electrochemical properties. Ex situ XRD analyses at different potentials in the lithiation/delithiation processes confirm a polymorphic phase transformation in the ZSS⊂NCNs. The synthesized ZSS⊂NCN enriched bimetallic selenide composites and the facile synthesis route provide a strategy for other bimetallic selenides, sulfide or phosphide composites with stable nanostructure to be utilized in energy storage.

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS2 Precipitation Dynamics and Phase Selection

Pyrite is the most abundant metal sulfide in the Earth’s crust and is also found on Mars. It can form by direct hydrothermal precipitation or by polymorphic phase transformation from marcasite. However, the control on the dynamics of hydrothermal pyrite precipitation is poorly understood, and the kinetics of the hydrothermal transformation from marcasite to pyrite is unknown. To address these issues, we quantified pyrite and marcasite formation in hydrothermal fluids at pH 1, using pyrrhotite as a precursor mineral to produce supersaturated solutions. In situ powder X-ray diffraction experiments at 190 °C showed that hydrothermal fluids rich in ΣS(-II) (0.2 molal) favored the precipitation of nanocrystal pyrite (∼20 nm) due to a high saturation index (>105), while ΣS(-II)-free fluids produced a mixture of marcasite and pyrite nanocrystals (21–46 nm) due to a low saturation index (<104). The fluid/rock ratio (70 and 120 g/g at 210 °C) can also affect the saturation indices of these fluids, influencing nucleation and crystal growth dynamics of pyrite and marcasite and resulting in complex evolution of crystallite size, phase abundance, and the pyrite/marcasite ratio. Ex situ hydrothermal experiments at 210 °C showed rapid transformation from marcasite to pyrite, with around 95% marcasite being transformed to pyrite in 20 weeks, compared to more than 6.3 million years at 210 °C under dry conditions based on extrapolation from previous kinetic studies. These results suggest that saturation index influences hydrothermal precipitation dynamics and controls phase selection between pyrite and marcasite and that marcasite may not survive over geological time in low-temperature (<200 °C), water-saturated environments.