Crystal Undergoes Phase Transition Research Articles

Programming the morphology of DNA origami crystals by magnesium ion strength

Harnessing the programmable nature of DNA origami for controlling structural features in crystalline materials affords opportunities to bring crystal engineering to a remarkable level. However, the challenge of crystallizing a single type of DNA origami unit into varied structural outcomes remains, given the requirement for specific DNA designs for each targeted structure. Here, we show that crystals with distinct equilibrium phases and shapes can be realized using a single DNA origami morphology with an allosteric factor to modulate the binding coordination. As a result, origami crystals undergo phase transitions from a simple cubic lattice to a simple hexagonal (SH) lattice and eventually to a face-centered cubic (FCC) lattice. After selectively removing internal nanoparticles from DNA origami building blocks, the body-centered tetragonal and chalcopyrite lattice are derived from the SH and FCC lattices, respectively, revealing another phase transition involving crystal system conversions. The rich phase space was realized through the de novo synthesis of crystals under varying solution environments, followed by the individual characterizations of the resulting products. Such phase transitions can lead to associated transitions in the shape of the resulting products. Hexagonal prism crystals, crystals characterized by triangular facets, and twinned crystals are observed to form from SH and FCC systems, which have not previously been experimentally realized by DNA origami crystallization. These findings open a promising pathway toward accessing a rich phase space with a single type of building block and wielding other instructions as tools to develop crystalline materials with tunable properties.

Dynamics of Organic Cations in Switchable Quinuclidinium Metal Chloride Dielectrics

The synthesis and structure of a series of quinuclidinium-based organic–inorganic hybrids of Q2CuCl4, Q2CoCl4, and Q4Pb3Cl10 are reported (Q = quinuclidinium, C7H13NH+). The dynamic disorder observed in the structure of quinuclidinium metal chlorides was investigated using variable-temperature single-crystal X-ray diffraction, IR, Raman, NMR, and dielectric spectroscopy. The crystals undergo phase transitions (PTs) where an order–disorder process takes place. However, it is assumed that in the case of Q2CoCl4 and Q2CuCl4, the reorientation of Q cations is a major force driving PT, while in Q4Pb3Cl10, the reorientation of inorganic ions (Pb–Cl moieties) is at least equally important. All three hybrid compounds exhibit switchable and tunable properties of the dielectric function between two stable ON/OFF states. The magnetic properties were also investigated over a wide temperature range by measuring the magnetic susceptibility and magnetization as a function of temperature and external magnetic field, which allowed us to demonstrate the competition between the paramagnetic and diamagnetic signals in these compounds. The dynamics probed by NMR has shown a nonequivalence of Q cations in all studied compounds.

Reversible colossal barocaloric effects near room temperature in 1-X-adamantane (X=Cl, Br) plastic crystals

Plastic crystals undergo phase transitions with unusually large volume and entropy changes related to strong molecular orientational disordering. These features have led to a resurgent interest in these materials because recently they have shown great potential in solid-state cooling applications driven by pressure. Here we demonstrate that two plastic crystals derived from adamantane -1-Br-adamantane and 1-Cl-adamantane- undergo colossal reversible barocaloric effects under moderate pressure changes in a wide temperature span near room temperature thanks to a relatively small hysteresis and very high sensitivity of the transition temperature to pressure. In particular, 1-Cl-adamantane displays an optimal operational temperature range covering from ~40 K below and up to room temperature, and under a pressure change of 1 kbar this compound outperforms any other barocaloric material known so far. Our work gives strong support to plastic crystals as best candidates for barocaloric cooling. We also provide insight into the physical origin of the entropy changes through the analysis of the disorder on the involved phases.

High pressure Raman spectroscopic study of phase transformations in Zn(CN)2

High-pressure Raman investigations in Zn(CN)2 has been reported up to a pressure of 10 GPa under hydrostatic and non-hydrostatic conditions. We observe several changes in the spectra including splitting of existing modes, broadening of Raman modes and sudden changes in the slope of the frequency vs pressure curve at ≈1 and 1.6 GPa which indicate that the crystal undergoes phase transitions at these pressures. The crystal amorphizes at the highest pressure of 10 GPa. On gradual pressure reduction and total pressure release, the sample doesnot return to its original phase. This indicates that Zn(CN)2 transforms irreversibly to an amorphous phase.

Record-high thermal stability achieved in a novel single-component all-organic ferroelectric crystal exhibiting polymorphism.

Traditionally, lead and heavy metal containing inorganic oxides dominate the area of ferroelectricity. Although, recently, lightweight non-toxic organic ferroelectrics have emerged as excellent alternatives, achieving higher temperature up to which the ferroelectric phase can persist has remained a challenge. Moreover, only a few of those are single-component molecular ferroelectrics and were discovered upon revisiting their crystal structures. Here we report a novel phenanthroimidazole derivative, which not only displays notable spontaneous and highly stable remnant polarizations with a low coercive field but also retains its ferroelectric phase up to a record-high temperature of ∼521 K. Subsequently, the crystal undergoes phase transition to form non-polar and centrosymmetric polymorphs, the first study of its kind in a single-component ferroelectric crystal. Moreover, the compound exhibits a significantly high thermal stability. Given the excellent figures-of-merit for ferroelectricity, this material is likely to find potential applications in microelectronic devices pertaining to non-volatile memory.

Field theory and anisotropy of a cubic ferromagnet near the Curie point

Critical fluctuations are known to change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, effective anisotropy acquires at T_c the universal value A* = v*/u* where u* and v* are coordinates of the cubic fixed point entering the scaling equation of state and expressions for nonlinear susceptibilities. In the paper, the numerical value of the anisotropy parameter A at the critical point is estimated using the \epsilon-expansion and pseudo-\epsilon-expansion techniques. Pade resummation of six-loop pseudo-$\epsilon$-expansions for u*, v*, and A* leads to the estimate A* = 0.13 close to that extracted from the five-loop \epsilon-expansion but differing considerably from the value A* = 0.089 given by the analysis of six-loop expansions of the \beta-functions themselves. This discrepancy is discussed and its roots are cleared up.

Anisotropy of a cubic ferromagnet at criticality.

Critical fluctuations change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, reduced anisotropy of nonlinear susceptibility acquires at T_{c} the universal value δ_{4}^{*}=2v^{*}/3(u^{*}+v^{*}) where u^{*} and v^{*} are coordinates of the cubic fixed point on the flow diagram of renormalization group equations. In the paper, the critical value of the reduced anisotropy is estimated within the pseudo-ε expansion approach. The six-loop pseudo-ε expansions for u^{*}, v^{*}, and δ_{4}^{*} are derived for the arbitrary spin dimensionality n. For cubic crystals (n=3) higher-order coefficients of the pseudo-ε expansions obtained turn out to be so small that use of simple Padé approximants yields reliable numerical results. Padé resummation of the pseudo-ε series for u^{*}, v^{*}, and δ_{4}^{*} leads to the estimate δ_{4}^{*}=0.079±0.006, indicating that detection of the anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is certainly possible.

Dielectric properties and phase transitions in crystals of TlInS x Se2 − x solid solutions

This paper reports on a study of the dielectric permittivity and electrical conductivity of single-crystal TlInS x Se2 − x solid solutions as functions of temperature and composition. It has been found that the dielectric permittivity ɛ and electrical conductivity σ decrease with increasing x and increase with growing temperature. The temperature dependences ɛ = f(T) and σ = f(T) for TlInS x Se2 − x crystals have been demonstrated to reveal anomalies in the form of maxima, which suggests that these crystals undergo phase transitions. The temperatures of the phase transitions increase with increasing x.

Structural characterization, phase transition and dielectric properties of 4-cyanopyridynium perchlorate monohydrate: [(4-CNC 5H 4NH)][ClO 4]·H 2O

Crystal structure of 4-cyanopyridynium perchlorate monohydrate ([(4-CNC 5H 4NH)][ClO 4]·H 2O) has been determined at 293 and 240 K as orthorhombic space group, Pnma and monoclinic space group, P2 1/ c, respectively, by means of single crystal X-ray diffraction. At room temperature the perchlorate anion reveals significant disorder, which is realized by the splitting of two oxygen atoms into four sites. DSC, dilatometric and dielectric spectroscopy techniques show that the crystal undergoes phase transition at 286/288 K (on cooling/heating scans). [(4-CNC 5H 4NH)][ClO 4]·H 2O appears to be an insulator with relatively high activation energy of the order of 100 kJ/mol. The phase transition in the title crystal is believed to be related to the dynamics of the perchlorate anion.

EPR of the CuBr 4(NH 3) 22− paramagnetic centre in ammonium bromide

Ammonium bromide crystals doped with Cu 2+ ions and grown from a basic solution have been studied at temperatures ranging from 4.2 to 300 K with Q-band EPR. The NH 4Br : Cu 2+ crystals grown under these conditions contain CuBr 4(NH 3) 2 2− paramagnetic centres showing sensibility to NH 4Br phase transitions. A detailed EPR study of this centre was conducted to determine some spin Hamiltonian parameters for the first time, as the NH 4Br : Cu 2+ crystals undergo phase transitions below room temperature. This study showed that the paramagnetic centre exhibited tetragonal symmetry at room temperature and below 78 K (a vestige of orthorhombic symmetry remained in this region), while at 78 K < T < 235 K the tetragonal and orthorhombic symmetries coexist. Models are mentioned for these two simultaneous symmetries.

Hydration and Pressure Effects on the Inter- and Intramolecular Vibrations of Tetramethylpyrazine Crystals

Abstract The Raman active inter- and intramolecular vibrations of tetramethylpyrazine and trihydrated tetramethylpyrazine crystals were studied under various pressures between 1 atm and 5 GPa. The pressure effect on the Raman frequency due to the intermolecular vibrations indicates that a tetramethylpyrazine crystal undergoes phase transitions under about 1.2 and 2.2 GPa and a trihydrated tetramethylpyrazine crystal undergoes phase transition under about 3.5 GPa. The pressure effect on the Raman frequency due to the intramolecular vibrations indicates that the pressure-induced frequency shift for the skeletal vibrations of trihydrated tetramethylpyrazine is larger than the corresponding shift of unhydrated tetramethylpyrazine, while the shift for the characteristic vibrations of the methyl groups of trihydrated tetramethylpyrazine is smaller than the corresponding shift of unhydrated tetramethylpyrazine. These observations suggest that the attractive force induced by the hydration plays a considerable role in the intermolecular interaction under high pressure in the molecular crystal, in addition to the repulsive force. The change of electron distribution, which strengthens the chemical bonds of the pyrazine ring more strongly than the bonds in the methyl groups, takes place with increasing pressure.

Phonon dispersion curves in dilute KTN crystals

The phonon dispersion curves of the transverse acoustic (TA) and the lowest transverse optic (TO) branches in the (001) direction of two (KTN) crystals with niobium concentrations of 0.8 and 1.2 at.% have been measured by inelastic neutron scattering at various temperatures. A pronounced temperature dependence has been observed for both the lowest TO phonon at the centre of the Brillouin zone and the TA phonons in the (001) direction for reduced wave vectors larger than 0.04. The temperature dependence of the TA phonons at large wavevectors shows a significant minimum. From the observation of this minimum it is conjectured that both crystals undergo phase transitions. The measured data have been analysed in the framework of a shell model with an anisotropic, nonlinear core - shell interaction. It is shown that the anomalous behaviour of the TA branch is due to an exchange of vibrational character between the phonons of the lowest TO branch and those of the TA branch. An estimate of the size of dipolar clusters around the niobium impurities is derived from the analysis of the dispersion of the lowest TO modes in the long-wavelength range.

Pressure Effect on the Inter- and Intramolecular Vibrations of Pyrazine Crystal

Abstract The effect of pressure on the Raman active inter- and intramolecular vibrations of the pyrazine crystal was studied under hydrostatic pressure up to 5 GPa. The frequency shift of the intermolecular vibrations and the discontinuous variation of the bandwidth of the ν2 and ν1 intramolecular vibrations induced by pressure at constant temperature indicate that the pyrazine crystal undergoes phase transition (change of the molecular orientation in the crystal) under about 1 GPa. The pressure-induced frequency shift of the intramolecular vibrations was calculated using an intermolecular potential of the atom–atom type. The calculation also suggests the occurrence of the phase transition of the crystal.

Ferroelastic Domain of (CH3NH3)4InCl7 and Its Phase Transitions

Optical observation of domain structure, differential thermal analysis, dielectric and dilatometric measurements of (CH 3 NH 3 ) 4 InCl 7 have been carried out over a temperature range from 25°C to 200°C. It has been found that the crystal undergoes phase transitions at 194°C ( T 1 ) and 190°C ( T 2 ), and is ferroelastic below T 1 . Taking account of the strain-compatibility relations for domain boundaries, it is suggested from the result of optical observation that the crystal symmetry is m m m , 2/ m and 2/ m in order of descending temperature.

Phase Transitions in (CH3NH3)4InBr7

Measurements of the dielectric constant, the DTA signal and the linear thermal expansion, optical observation of domain structure and X-ray examination of (CH 3 NH 3 ) 4 InBr 7 have been carried out over a temperature range from 25°C to 180°C. It is found that the crystal undergoes phase transitions at 171°C ( T 1 ) and 141°C ( T 2 ), and is ferroelastic below T 1 . The crystal at room temperature belongs to monoclinic P2/ n with lattice parameters: a =16.854(6) A, b =7.731(6) A, c =16.756(9) A and β=103.22(2)°. When the symmetry is approximated as to be pseudo-orthorhombic by taking a ′ = a + c , b ′ = b and c ′ = c - a (β ′ =90.34(11)°), the domain structure observed below T 1 is deduced from the strain-compatibility relations for the domain boundaries by taking account of the symmetry change from mmm to 2/ m at T 1 . At T 2 no change of domain configuration has been detected.

The model of phase transitions in the crystals of the NH4HSeO4 type

Abstract NH4HSeO4 crystals and their deuterated analogs undergo phase transitions and posess a number of interesting properties. Experimental investigations of the crystals by NMR, X-ray diffraction, optical and other methods were realized in 1-4: All crystals have a high temperature phase of still not defined symmetry. In this phase an increase of proton conductivity is observed 2. With temperature decrease the NH4HSeO4 crystals undergo the successive phase transitions: into paraelectric phase (space group I1) at Tc1=417 K; into incommensurate phase at Tci=261 K, into ferroelectric phase (space group I2) at Tc3=98 K. There are three molecules per unit cell in monoclinic and triclinci phases 1. Monoclinic phase at temperatures below T=271 K, incommensurate and apprently ferroelectric phases are unstable since after being for several hours in this temperature region the crystal undergoes phase transition into orthorhombic phase (P212121) and turns to have four molecules per unit cell 3,4. The orthorhombic phase is observed for deuterated crystals with deuterium concentration higher thant 45% below Tc2=305 K. In temperature region Tc2>T>Tc1 ND4DSeO4 has momoclinic structure with the space group I2 (Z=3). The phase (x, T) diagram of N(H1-xDx)4 H1-xDxSeO4 is shown in Fig.1. Dependently on the conditions the crystal can have one of two following successions of phase transitions: superionic phase → monocolinic phase → orthorhombic phase; superionic phase → monoclinic phase → incommensurate phase → ferroelectric phase → low-temperature phase

Ferroelectric Properties of N(CH3)4HSO4·H2O

The ferroelectricity in the crystal obtained by the evaporation of aqueous solution of N(CH3)4HSO4 has already been reported by us. Recently, by the thermo-gravity analysis, it was found that most of the crystals are the hydrated crystal N(CH3)4HSO4·H2O containing one molecule of water of crystallization and that some crystals contain only about 0.3 molecule. The latter crystals are considered to be mixture of the hydrated crystal and the completely anhydrous one N(CH3)4HSO4, which has not been obtained yet. The hydrated crystal undergoes phase transitions at -104°C and around 40°C, and the completely anhydrous crystal can be said to show transitions around -70, -42, 42 and 129°C. The former shows the ferroelectricity in the temperature range from -104°C to about 40°C and the latter seems to show also the ferroelectricity in nearly the same temperature range.

Pyroelectric properties of langbeinite-type K2Zn2(SO4)3

Abstract Pyroelectric measurements have been made on K2Zn2(SO4)3 crystals with simultaneous optical examination of the domain structure of the specimen. The crystal undergoes phase transitions at 136 K and 85 K. Dielectric hysteresis measurement reveals ferroelectricity in the temperature range 85 K < T < 136 K. Anomalous temperature dependence of the spontaneous polarization is observed in the ferroelectric phase. Below 85 K, no pyroelectricity is obtained, and there are found three types of domains, all in parallel extinction. The crystal systems and point groups of the low temperature phases are determined as monoclinic 2 for 85 K < T < 136 K and orthorhombic 222 for T < 85 K.

Raman and infrared spectra of ferroelectric (CH3NH2CH2COO)3 CaCl2

AbstractRaman spectrum of Tris‐sarcosine Calcium chloride has been recorded both in the para and ferroelectric phases using λ = 2537 Å of mercury as exciting radiation. The infrared absorption spectrum has been recorded both above and below the Curie temperature, in the region 400 to 4000 cm−1. From the observed splitting of the infrared bands it is concluded that the second order ferroelectric phase transition at 127K is due to a dynamical ordering of sarcosine molecules which exist in zwitteron configuration. Raman spectrum shows eight lattice lines which do not exhibit any anomaly as the crystal undergoes phase transition.