The world needs clean energy. One of the most promising ways of producing it in large amounts is the helium3-deuterium (3He-D) fusion reaction. Although there are numerous sources of 3He on Earth, most of them are either difficult to access or unprofitable to operate. The main problem underlying the shortage of 3He is the lack of an effective method of obtaining this isotope. Here we report the results of quantum filtration of 3He from liquid helium in a superfluid state (below the λ-transition), with the use of an entropy filter made of a high-temperature superconductor YBCO-123. During the operation of so-called fountain effect generated with this filter, unlike the other filters, we observed a strong increase of 3He concentration downstream, where only pure 4He was expected. This effect occurred due to the unique combination of two quantum phenomena –superfluidity and superconductivity, leading to the observation of a low-temperature rectification-like process. This process would be considerably more economical than filtration, as rectification could be operated above the λ-transition. Moreover, micro-superconductors could be applied also to the extraction of deuterium, thus allowing the same method to be used for both crucial components of the 3He-D fusion. This method should be easy to upscale and could be used in space (with less energy input) as 3He, the crucial isotope for future energy, is also sought beyond the Earth.

The dielectric response of M-hexaferrite nanoceramics is complex since it is determined by crystal structure and microstructure. We studied the dielectric behavior of Nd3+ modified Sr2 + Fe12O19 nanoceramics with ferric ions, responsible for magnetic properties, substituted by Sc3+ and Al3+. To compare the effect of different ionic radii we discussed the dielectric response of Sr0.95Nd0.05Fe12-xScxO19 and Sr0.95Nd0.05Fe12-xAlxO19 at the doping level of x = 1.08. The dielectric response was found to consist of four contributions: (i) Low-temperature dispersion of dielectric polarization created by doping-induced spin-canting. The polarization, described by the inverse Dzyaloshinskii-Moriya model, is in nanoceramics limited by the shape and size of the crystallites. (ii) Changes in relaxation modes of polar vacancies due to interaction with electric dipole moments modified by deformation of oxygen octahedra. (iii) Dielectric dispersion in room temperature range related to space charge relaxation in grain boundaries. (iv) High-temperature electric conductivity of the grain interiors.

The dielectric response of M-hexaferrite nanoceramics is complex since it is determined by crystal structure and microstructure. We studied the dielectric behavior of Nd3+ modified Sr2 + Fe12O19 nanoceramics with ferric ions, responsible for magnetic properties, substituted by Sc3+ and Al3+. To compare the effect of different ionic radii we discussed the dielectric response of Sr0.95Nd0.05Fe12-xScxO19 and Sr0.95Nd0.05Fe12-xAlxO19 at the doping level of x = 1.08. The dielectric response was found to consist of four contributions: (i) Low-temperature dispersion of dielectric polarization created by doping-induced spin-canting. The polarization, described by the inverse Dzyaloshinskii-Moriya model, is in nanoceramics limited by the shape and size of the crystallites. (ii) Changes in relaxation modes of polar vacancies due to interaction with electric dipole moments modified by deformation of oxygen octahedra. (iii) Dielectric dispersion in room temperature range related to space charge relaxation in grain boundaries. (iv) High-temperature electric conductivity of the grain interiors.

We report the existence of a low-temperature polar phase in PbZrO3 below 270 K. The temperature depen-dence of resultant polarization was assigned from pyroelectric current changes measured after poling the single crystal or ceramic in a DC electric field. This was observed in single crystals and ceramics and may have a connection with the presence of polar (ferrielectric) antiphase boundaries inside the antiferroelectric phase. The transition point is demonstrated by changes in domain structure and anomalies in dielectric permittivity and losses in as-grown single crystals and ceramic samples.

K1-xLixTaO3 (x = 0.043, 0.08) crystals, characterized by pyroelectric current with calculated spontaneous polarization and zero-field second-harmonic generation, have been studied by broadband dielectric spectroscopy, including time-domain terahertz transmission and infrared (IR) reflectivity, and by polarized Raman spectroscopy in the 10-300 K temperature range. This multiexperimental approach has proven the percolative nature of the ferroelectric (FE) transition at low temperatures and demonstrated that the FE phase is inherently inhomogeneous and displays coexistence of FE and relaxor regions. Thanks to the very broad frequency range studied (from 1 Hz to 20 THz), the relevant excitations were identified and fitted in the dielectric response of both crystals: three relaxations, a central mode (CM), and a soft mode (SM) that splits into three components on cooling. Two Cole-Cole relaxations (assigned to flipping of polar nanoregions around the Li+ ions by pi/2 and pi, in agreement with the known literature), thermally activated below similar to 150 K, but staying in the gigahertz range at higher temperatures, do not show any frequency anomaly at the FE transition and are therefore related to the non-FE parts of the sample volume. A third thermally activated relaxation of unusually slow dynamics was revealed at low frequencies and preliminary assigned to an expected critical relaxation connected with the percolative nature of the FE phase transition. The IR SM, which undergoes much less softening than in the undoped KTaO3, splits into three components below the FE transition. Two higher-frequency components correspond to the FE volume part of the crystals assigned to the split A(1) and E modes due to the cubic-tetragonal transition. The third low-frequency component is assigned to the non-FE (relaxor) volume part. Our assignment was confirmed by modeling the terahertz-IR response of the SM using the Bruggeman model within the effective medium approach. Below the SM response, an additional CM in the 10(11) Hz range in the whole temperature range is inferred from the fits.

The 3He isotope finds applications in many areas of science and industry, the most important of which are cryogenics, where 3He allows for achieving millikelvins in dilution refrigerators, and public security with 3He detectors of radioactive materials at airports and important buildings. 3He is also used in medicine for lung tomography. One of the most extraordinary future applications is the use of 3He in fusion reactors for clean energy. 3He is currently very expensive, with prices reaching USD 2750 for 1 liter of gas in normal conditions; thus, more effort is put into finding economically viable methods to acquire this isotope. The article shows research results of acquiring the 3He isotope from liquid helium by a quantum separation method with the use of entropy filters based on new carbon nanomaterials: purified multiwall carbon nanotubes (MWCNTs) and purified multiwall carbon nanotubes decorated with ZrO2 nanoparticles. MWCNTs were bundled and applied in the form of pressed tablets with fixed sizes. The research was conducted at the low-temperature region, where helium exhibits its quantum properties by undergoing a phase transition to the superfluid phase at the lambda temperature: Tλ= 2.18 K. Entropy filters work below this temperature.

Helium is the second most abundant element in the Universe after hydrogen. Considerable resources of helium-3 isotope (He3) are located mostly outside the Earth. He3 is very important for science and industry, especially for airport neutron detectors, lung tomography and helium dilution refrigerators. Besides, global warming is forcing the industry and governments to search for alternative energy sources, and He3 has the potential to be used as fuel in future nuclear fusion power plants. Unfortunately, the price of gaseous He3 has recently increased from $200 per liter to over $2750. The expected further increase in price and demands led us to present an analysis of the economic profitability for He3 separation process, which utilizes the properties of superfluid helium. This paper shows the arguments supporting the idea that extraction from natural sources is the only economically viable way of obtaining He3 isotope nowadays. The method could be relatively easily implemented into the production cycles of the low temperature natural gas purification plant.

The results of measurements of low-temperature susceptibility: linear and nonlinear, and polarization under dc electric field of the lithium-doped potassium tantalate K0.92Li0.08TaO3 (KLT-8%Li) solid solution are presented. The recognized coexistence of the relaxor-like and ferroelectric behavior is presented. The observed ferroelectric phase transition is of the first-order type. Using an external dc electric field Edc = 178 kV/m the temperature of the ferroelectric phase transition is shifted by 3 K toward the value of 117 K, relative to the TC = 114 K observed without external dc electric field. Experimental facts reported in the present paper allowed us to argue that ferroelectricity in K1-xLixTaO3, in the case of x > 0.022 is due to a dynamical correlation of the off-center motions of Ta+5 ions in the octahedral environment of oxygen ions and does not arise directly as a result of the ordering of Li+ ion dipole moments within the so-called polar nanoregions.

We present the method of the liquid helium enrichment with He3 isotope based on a special solution of the helium bath cryostat (251 LHe) equipped with the heat exchanger and entropy filter to stimulate quantum filtration process in low temperature region. The cryostat design makes it possible to increase the initial concentration of He3 more than one order of magnitude. While the temperature of lambda point was achieved close to the capillary-equipped heat exchanger, the movement of lambda front within the liquid helium is observed. A consistent description of the various stages of the cryostat operation with cooling process above the lambda transition, during the long period of lambda front movement and in a superfluid region, with the acquisitioning of He3 isotope in all of these regions, is devoted to the design of a helium isotope flow-separator on an industrial scale.

Recently reported magnetic quantum paraelectric properties in M-type hexaferrite single crystals have encouraged us to study the dielectric response of SrFe12O19 nanocrystallites down to the temperature of 10 K. As Sc-induced multiferroicity, promising for electromagnetic control, has been reported in bulk and films of hexaferrites, we also studied the size effect in dielectric response of Sr0.95Nd0.05Fe12-xScxO19 nanocrystallites with x = 0.36, 1.08, and 1.56. The nanopowders were obtained by citric method and the phase purity and the microstructure were controlled using X-ray diffraction and scanning electron microscopy. No clear evidence of quantum paraelectric behavior has been observed in temperature variation of dielectric permittivity of SrFe12O19 nanopowder. In the case of Nd-stabilized Sc-doped nanocrystallites, a low-temperature dielectric relaxation, similar to that in dipolar glasses, has been discovered. Activation energy of 62.5 meV was obtained for the lowest doping level and a modest increase in the energy was found at higher Sc concentrations. We relate the low-temperature relaxation in Sc-doped hexaferrite nanopowder to dielectric displacive polarization at the 4e Wyckoff sites modified by Sc-ions substituting the ferric ions in 4f2 and 12k positions.

The results of low-temperature linear and nonlinear susceptibilities, polarization measurements and the dc electric field dependence of the dielectric properties of the lithium-doped potassium tantalate K1-xLixTaO3, x = 0.034 (KLT-3.4%Li) solid solution are presented. The coexistence of the relaxor-like and ferroelectric behavior and different mechanisms leading to either of them are discussed. The observed ferroelectric phase transition is of the first-order type with temperature hysteresis. This transition is due to the off-center motions of Ta ions in the octahedral environment of oxygen ions. Clusters of Li+ ions produce a relaxor-like behavior and random electric field. This field reduces the depolarization field and allows off-center motions of Ta ions and an appearance of spontaneous polarization.

The results of low-temperature linear and nonlinear susceptibilities and polarization measurements of the KLT-4.3%Li crystalline sample are presented. The following model of the mechanism of the ferroelectricity in the K0.957Li0.043TaO3 (KLT-4.3%Li) solid solution is proposed. Static quasi-frozen clusters of Li+ dipoles affect the ordering process of the remainder of the system: a dynamical correlation of the off-center motions of Ta ions along one of the equivalent off-center sites in the < 111 > cubic direction in the octahedral environment of O ions occurs and leads to the formation of a reversible spontaneous polarization. (C) 2016 Elsevier Ltd. All rights reserved.

The results of low-temperature linear and nonlinear susceptibilities, polarization measurements of the dielectric properties of the KTaO3 and K1-xLixTaO3, x=0.02 and 0.08 solid solution are presented. The coexistence of the relaxor-like and ferroelectric behavior and different mechanisms leading to either of them are discussed. The observed ferroelectric phase transition in K1-xLixTaO3, x=0.08 is of the first-order type with temperature hysteresis. Clusters of Li+ ions produce a relaxor-like behavior and random electric field. The ferroelectric phase transition is due to the off-center motions of Ta ions in the octahedral environment of oxygen ions. This process leads to the formation of a reversible spontaneous polarization.

The results of low‐temperature linear as well as nonlinear and electric susceptibility and polarization P measurements of the K1–xLixTaO3, x = 0.01 crystal are presented. A coexistence of two different phases within a temperature range where the glassy state sets in is proposed. In the current work, we have proved the existence of an electric field‐revealed precursor ferroelectric phase without low‐frequency relaxation. With decreasing temperature, the second‐order nonlinear electric susceptibility, , which is proportional to the polarization P, increases from zero at about 40 K to at 4.2 K. This behavior is independent of the frequency of the ac probing electric field, and thus discloses the existence of a newly observed polarization component.

The results of an investigation of dielectric properties of perovskite-type single crystals with solid solutions of potassium-lithium tantalate K1-xLixTaO3 are presented. Particular attention is focused on two selected concentrations of x, 2% and 4.3%, which are representative for the samples with lower and higher concentration of lithium ions, respectively. While a peak in dielectric losses, as observed at higher temperature, has just been revealed for low Li content, it becomes well developed for high lithium concentration. In such crystals there exist noticeable oxygen vacancies, and additional defects associated with lithium ions have a great influence on the dielectric losses in low temperature scope. The consideration pertains to the temperature dependence of the activation energy of the possible polaronic state in the context of lithium ion content.

Linear and nonlinear dielectric properties of nominally pure quantum paraelectric potassium tantalate KTaO3 crystals are presented. By use experimental technique to get the higher order electric susceptibility χ2, and χ3, in addition to the linear one, χ1, dielectric loss factor, and the polarization, obtained by integrating the depolarization current measured on zero field heating (ZFH) after field cooling (FC) run, we have proved existence of polar nanoregions (PNR׳s for short) below 40K in nominally pure potassium tantalate KTaO3 single crystal.

As demands on 3He are increasing and conventional 3He production through tritium decay is decreasing, alternative 3He production methods are becoming economically viable. One such possibility is to use entropy filters for extraction of the 3He isotope from natural gas. According to the phase diagram of the 3He, its solidification is impossible by only lowering of the temperature. Hence during the cooling process at stable pressure we can reach lambda-point and pass to the special phase - He II. The total density of HeII is a sum of the two phases: normal the superfluid ones. It is possible to separate these two phases with an entropy filter - the barrier for the classically-behaving normal phase. This barrier can also be used to separate the two main isotopes of He: 4He and 3He, because at temperatures close to the 4He-lambda-point the 3He isotope is part of the normal phase. The paper presents continuous flow schemes of different separation methods of 3He from helium commodity coming from natural gas cryogenic processing. An overall thermodynamic efficiency of the 3He/4He separation process is presented. A simplified model of continuous flow HeI -HeII recuperative heat exchanger is given. Ceramic and carbon porous plugs have been tested in entropy filter applications.

Temperature dependences of the longitudinal permittivity, piezoelectric coefficient d 36, and elastic constant c 66 E of K1 − x (NH4) x H2PO4 mixed crystals are studied experimentally. A microscopic model is proposed for crystals of the K1 − x (NH4) x H2PO4 type that includes the piezoelectric contribution to the effective pseudospin cluster Hamiltonian. Dielectric elastic and electromechanical properties of these crystals with ammonium concentrations x below 0.40 are calculated in a wide temperature range using the cluster approach. The calculation results are in qualitative agreement with experimental data.