Ice XI is the hydrogen-ordered form of Ih, the ordinary form of ice. Different phases of ice, from ice II to ice XIX, have been created in the laboratory at different temperatures and pressures. The total internal energy of ice XI is about one sixth lower than ice Ih, so in principle it should naturally form when ice Ih is cooled to below 72 K. The low temperature required to achieve this transition is correlated with the relatively low energy difference between the two structures. [1] Water molecules in ice Ih are surrounded by four semi-randomly directed hydrogen bonds. Such arrangements should change to the more ordered arrangement of hydrogen bonds found in ice XI at low temperatures, so long as localized proton hopping is sufficiently enabled; a process that becomes easier with increasing pressure. [2] Correspondingly, ice XI is believed to have a triple point with hexagonal ice and gaseous water at (~72 K, ~0 Pa).
Ice XI has an orthorhombic structure with space group Cmc21 containing eight molecules per unit cell. Its lattice parameters are a=4.465(3) Å, b=7.859(4) Å, and c=7.292(2) Å at 5 K. [3] [4] There are actually 16 crystallographically inequivalent hydrogen-ordered configurations of ice with an orthorhombic structure of eight atoms per unit cell, but electronic structure calculations show Cmc21 to be the most stable. [5] [6] Another possible configuration, with space group Pna21 is also of interest, as it is an antiferroelectric crystal, which Davidson and Morokuma incorrectly suggested as the most stable structure in 1984. [7]
In practice, ice XI is most easily prepared from a dilute (10 mM) KOH solution kept just below 72 K for about a week (for D2O a temperature just below 76 K will suffice). [8] [9] The hydroxide ions create defects in the hexagonal ice, allowing protons to jump more freely between the oxygen atoms (and so this structure of ice XI breaks the 'ice rules'). More specifically, each hydroxide ion creates a Bjerrum L defect and an ionized vertex. Both the defect and the ion can move throughout the lattice and 'assist' with proton reordering. The positive K+ ion may also play a role because it is found that KOH works better than other alkali hydroxides. [10] The exact details of these ordering mechanisms are still poorly understood and under question because experimentally the mobility of the hydroxide and K+ ions appear to be very low around 72 K. [11] [12] The current belief is that KOH acts only to assist with the hydrogen reordering and is not required for the lower-energy stability of ice XI. However, calculations by Toshiaki Iitaka in 2010 call this into question. [13] Iitaka argues that the KOH ions compensate for the large net electric dipole moment of the crystal lattice along the c-axis. The aforementioned electronic structure calculations are done assuming an infinite lattice and ignore the effects of macroscopic electric fields created by surface charges. Because such fields are present in any finite size crystal, in non-doped ice XI, domains of alternating dipole moment should form as in conventional ferroelectrics. [13] It has also been suggested that the ice Ih => ice XI transition is enabled by the tunneling of protons. [14]
Although ice XI is thought to be a more stable conformation than ice Ih, the transformation is very slow. According to one report, in Antarctic conditions it is estimated to take at least 100,000 years to form without the assistance of catalysts.[ citation needed ] Ice XI was sought and found in Antarctic ice that was about 100 years old in 1998. [15] A further study in 2004 was not able to reproduce this finding, however, after studying Antarctic ice which was around 3000 years old. [16] The 1998 Antarctic study also claimed that the transformation temperature (ice XI => ice Ih) is −36 °C (237 K), which is far higher than the temperature of the expected triple point mentioned above (72 K, ~0 Pa). Ice XI was also found in experiments using pure water at very low temperature (~10 K) and low pressure – conditions thought to be present in the upper atmosphere. [17] Recently, small domains of ice XI were found to form in pure water; its phase transition back to ice Ih occurred at 72 K while under hydrostatic pressure conditions of up to 70 MPa. [18]
Ice Ih that has been transformed to ice XI and then back to ice Ih, on raising the temperature, retains some hydrogen-ordered domains and more easily transforms back to ice XI again. [19] A neutron powder diffraction study found that small hydrogen-ordered domains can exist up to 111 K. [20]
There are distinct differences in the Raman spectra between ices Ih and XI, with ice XI showing much stronger peaks in the translational (~230 cm−1), librational (~630 cm−1) and in-phase asymmetric stretch (~3200 cm−1) regions. [21] [22]
Ice Ic also has a proton-ordered form. The total internal energy of ice XIc was predicted as similar as ice XIh [23]
Hints of hydrogen-ordering in ice had been observed as early as 1964, when Dengel et al. attributed a peak in thermo-stimulated depolarization (TSD) current to the existence of a proton-ordered ferroelectric phase. [24] However, they could not conclusively prove that a phase transition had taken place, and Onsager pointed out that the peak could also arise from the movement of defects and lattice imperfections. Onsager suggested that experimentalists look for a dramatic change in heat capacity by performing a careful calorimetric experiment. A phase transition to ice XI was first identified experimentally in 1972 by Shuji Kawada and others. [25] [26] [27]
Ice XI is ferroelectric, meaning that it has an intrinsic polarization. To qualify as a ferroelectric it must also exhibit polarization switching under an electric field, which has not been conclusively demonstrated but which is implicitly assumed to be possible. Cubic ice also has a ferrolectric phase and in this case the ferroelectric properties of the ice have been experimentally demonstrated on monolayer thin films. [28] In a similar experiment, ferroelectric layers of hexagonal ice were grown on a platinum (111) surface. The material had a polarization that had a decay length of 30 monolayers suggesting that thin layers of ice XI can be grown on substrates at low temperature without the use of dopants. [29] One-dimensional nano-confined ferroelectric ice XI was created in 2010. [30]
As was mentioned, ice XI can theoretically form at low pressures at temperatures between 50–70 K – temperatures present in astrophysical environments of the outer solar system and within permanently shaded polar craters on the Moon and Mercury. Ice XI forms most easily around 70 K – paradoxically, it takes longer to form at lower temperatures. Extrapolating from experimental measurements, it is estimated to take ~50 years to form at 70 K and ~300 million years at 50 K. [31] It is theorized to be present in places like the upper atmospheres of Uranus and Neptune [20] and on Pluto and Charon. [31]
Small domains of ice XI could exist in the atmospheres of Jupiter and Saturn as well. [20] The fact that small domains of ice XI can exist at temperatures up to 111 K has some scientists speculating that it may be fairly common in interstellar space, with small 'nucleation seeds' spreading through space and converting regular ice, much like the fabled ice-nine mentioned in Vonnegut's Cat's Cradle . [20] [32] The possible roles of ice XI in interstellar space [31] [33] and planet formation [34] have been the subject of several research papers. Until observational confirmation of ice XI in outer space is made, the presence of ice XI in space remains controversial owing to the aforementioned criticism raised by Iitaka. [13] The infrared absorption spectra of ice XI was studied in 2009 in preparation for searches for ice XI in space. [35]
In chemistry, a hydrogen bond is primarily an electrostatic force of attraction between a hydrogen (H) atom which is covalently bonded to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Such an interacting system is generally denoted Dn−H···Ac, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are the period 2 elements nitrogen (N), oxygen (O), and fluorine (F).
Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.
In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the cation [H3O]+, also written as H3O+, the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton (a positive hydrogen ion, H+) to the surrounding water molecules (H2O). In fact, acids must be surrounded by more than a single water molecule in order to ionize, yielding aqueous H+ and conjugate base. Three main structures for the aqueous proton have garnered experimental support: the Eigen cation, which is a tetrahydrate, H3O+(H2O)3, the Zundel cation, which is a symmetric dihydrate, H+(H2O)2, and the Stoyanov cation, an expanded Zundel cation, which is a hexahydrate: H+(H2O)2(H2O)4. Spectroscopic evidence from well-defined IR spectra overwhelmingly supports the Stoyanov cation as the predominant form. For this reason, it has been suggested that wherever possible, the symbol H+(aq) should be used instead of the hydronium ion.
Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash.
The self-ionization of water (also autoionization of water, and autodissociation of water, or simply dissociation of water) is an ionization reaction in pure water or in an aqueous solution, in which a water molecule, H2O, deprotonates (loses the nucleus of one of its hydrogen atoms) to become a hydroxide ion, OH−. The hydrogen nucleus, H+, immediately protonates another water molecule to form a hydronium cation, H3O+. It is an example of autoprotolysis, and exemplifies the amphoteric nature of water.
Ice Ih is the hexagonal crystal form of ordinary ice, or frozen water. Virtually all ice in the biosphere is ice Ih, with the exception only of a small amount of ice Ic that is occasionally present in the upper atmosphere. Ice Ih exhibits many peculiar properties that are relevant to the existence of life and regulation of global climate. For a description of these properties, see Ice, which deals primarily with ice Ih.
Monopotassium phosphate (MKP) (also, potassium dihydrogen phosphate, KDP, or monobasic potassium phosphate) is the inorganic compound with the formula KH2PO4. Together with dipotassium phosphate (K2HPO4.(H2O)x) it is often used as a fertilizer, food additive, and buffering agent. The salt often cocrystallizes with the dipotassium salt as well as with phosphoric acid.
Ice IX is a form of solid water stable at temperatures below 140 K or -133.15 C and pressures between 200 and 400 MPa. It has a tetragonal crystal lattice and a density of 1.16 g/cm3, 26% higher than ordinary ice. It is formed by cooling ice III from 208 K to 165 K. Its structure is identical to ice III other than being completely proton-ordered.
Bismuth ferrite (BiFeO3, also commonly referred to as BFO in materials science) is an inorganic chemical compound with perovskite structure and one of the most promising multiferroic materials. The room-temperature phase of BiFeO3 is classed as rhombohedral belonging to the space group R3c. It is synthesized in bulk and thin film form and both its antiferromagnetic (G type ordering) Néel temperature (approximately 653 K) and ferroelectric Curie temperature are well above room temperature (approximately 1100K). Ferroelectric polarization occurs along the pseudocubic direction () with a magnitude of 90–95 μC/cm2.
Ice Ic is a metastable cubic crystalline variant of ice. Hans König was the first to identify and deduce the structure of ice Ic. The oxygen atoms in ice Ic are arranged in a diamond structure and is extremely similar to ice Ih having nearly identical densities and the same lattice constant along the hexagonal puckered-planes. It forms at temperatures between 130 and 220 kelvins upon cooling, and can exist up to 240 K (−33 °C) upon warming, when it transforms into ice Ih.
Ice VII is a cubic crystalline form of ice. It can be formed from liquid water above 3 GPa (30,000 atmospheres) by lowering its temperature to room temperature, or by decompressing heavy water (D2O) ice VI below 95 K. (Different types of ice, from ice II to ice XVIII, have been created in the laboratory at different temperatures and pressures. Ordinary water ice is known as ice Ih in the Bridgman nomenclature.) Ice VII is metastable over a wide range of temperatures and pressures and transforms into low-density amorphous ice (LDA) above 120 K (−153 °C). Ice VII has a triple point with liquid water and ice VI at 355 K and 2.216 GPa, with the melt line extending to at least 715 K (442 °C) and 10 GPa. Ice VII can be formed within nanoseconds by rapid compression via shock-waves. It can also be created by increasing the pressure on ice VI at ambient temperature. At around 5 GPa, Ice VII becomes the tetragonal Ice VIIt.
Ice II is a rhombohedral crystalline form of ice with a highly ordered structure. It is formed from ice Ih by compressing it at a temperature of 198 K at 300 MPa or by decompressing ice V. When heated it undergoes transformation to ice III. Ordinary water ice is known as ice Ih,. Different types of ice, from ice II to ice XIX, have been created in the laboratory at different temperatures and pressures. It is thought that the cores of icy moons like Jupiter's Ganymede may be made of ice II.
Ice XV is a crystalline form of ice, a partially proton-ordered form of ice VI. It is created by cooling hydrochloric-acid-doped ice VI to around 130 K at 1 GPa.
In statistical mechanics, the ice-type models or six-vertex models are a family of vertex models for crystal lattices with hydrogen bonds. The first such model was introduced by Linus Pauling in 1935 to account for the residual entropy of water ice. Variants have been proposed as models of certain ferroelectric and antiferroelectric crystals.
Water is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound and is described as the "universal solvent" and the "solvent of life". It is the most abundant substance on the surface of Earth and the only common substance to exist as a solid, liquid, and gas on Earth's surface. It is also the third most abundant molecule in the universe.
In chemistry, ice rules are basic principles that govern arrangement of atoms in water ice. They are also known as Bernal–Fowler rules, after British physicists John Desmond Bernal and Ralph H. Fowler who first described them in 1933.
A Bjerrum defect is a crystallographic defect which is specific to ice, and which is partly responsible for the electrical properties of ice. It was first proposed by Niels Bjerrum in 1952 in order to explain the electrical polarization of ice in an electric field. A hydrogen bond normally has one proton, but a hydrogen bond with a Bjerrum defect will have either two protons or no proton. D-defects are more energetically favorable than L-defects. The unfavorable defect strain is resolved when a water molecule pivots about an oxygen atom to produce hydrogen bonds with single protons. Dislocations of ice Ih along a slip plane create pairs of Bjerrum defects, one D defect and one L defect.
Caesium bisulfate or cesium hydrogen sulfate is an inorganic compound with the formula CsHSO4. The caesium salt of bisulfate, it is a colorless solid obtained by combining Cs2SO4 and H2SO4.
Solid nitrogen is a number of solid forms of the element nitrogen, first observed in 1884. Solid nitrogen is mainly the subject of academic research, but low-temperature, low-pressure solid nitrogen is a substantial component of bodies in the outer Solar System and high-temperature, high-pressure solid nitrogen is a powerful explosive, with higher energy density than any other non-nuclear material.
Ice IV is a metastable high-pressure phase of ice. It is formed when liquid water is compressed with an immense force.
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