Magnetic Gaps related to Spin Glass Order in Fermionic Systems

We provide evidence for spin glass related magnetic gaps in the fermionic density of states below the freezing temperature. Model calculations are presented and proposed to be relevant for explaining resistivity measurements which observe a crossover from variable-range- to activated behavior. The magnetic field dependence of a hardgap and the low temperature decay of the density of states are given. In models with fermion transport a new metal-insulator transition is predicted to occur due to the spin-glass gap, anteceding the spin glass to quantum paramagnet transition at smaller spin density. Important fluctuation effects due to finite range frustrated interactions are estimated and discussed.Comment: 4 pages, 1 Postscript figure, revised version accepted for publication in Physical Review Letter

One-dimensional transport in polymer nanofibers

We report our transport studies in quasi one-dimensional (1D) conductors - helical polyacetylene fibers doped with iodine and the data analysis for other polymer single fibers and tubes. We found that at 30 K < T < 300 K the conductance and the current-voltage characteristics follow the power law: G(T) ~ T^alpha with alpha ~ 2.2-7.2 and I(V) ~ V^betta with betta ~ 2-5.7. Both G(T) and I(V) show the features characteristic of 1D systems such as Luttinger liquid or Wigner crystal. The relationship between our results and theories for tunneling in 1D systems is discussed.Comment: 11 pages, 3 figures, accepted for publication in Phys. Rev. Letter

Effect of electric field on the photoluminescence of polymer-inorganic nanoparticles composites

We report on the effect of electric field on the photoluminescence, PL, from a composite consisting of a conjugated polymer mixed with zinc oxide nanoparticles. We have found that in the absence of electric field PL emission from the composite film has two maxima in the blue and green-yellow regions. Application of a voltage bias to planar gold electrodes suppresses the green-yellow emission and shifts the only PL emission maximum towards the blue region. Current-voltage characteristics of the polymer-nanoparticles composite exhibit the non-linear behavior typical of non-homogeneous polymer-inorganic structures. Generation of excited states in the composite structure implies the presence of several radiative recombination mechanisms including formation of polymer-nanoparticle complexes including exciplex states and charge transfer between the polymer and nanoparticle that can be controlled by an electric field.Comment: 5 pages, 5 figures. accepted for publication in Solid State Communication

Thermodynamic aspects of materials' hardness: prediction of novel superhard high-pressure phases

In the present work we have proposed the method that allows one to easily estimate hardness and bulk modulus of known or hypothetical solid phases from the data on Gibbs energy of atomization of the elements and corresponding covalent radii. It has been shown that hardness and bulk moduli of compounds strongly correlate with their thermodynamic and structural properties. The proposed method may be used for a large number of compounds with various types of chemical bonding and structures; moreover, the temperature dependence of hardness may be calculated, that has been performed for diamond and cubic boron nitride. The correctness of this approach has been shown for the recently synthesized superhard diamond-like BC5. It has been predicted that the hypothetical forms of B2O3, diamond-like boron, BCx and COx, which could be synthesized at high pressures and temperatures, should have extreme hardness

Активационные процессы при работе ионного мемристора Ag/SnSe/Ge2Se3/W с самоформирующимся токопроводящим каналом

In an Ag/SnSe/Ge2Se3/W ionic type memristor, the activation energy of two main processes responsible for its operation has been determined, namely: the activation energy for the formation of a conductive channel and the activation energy for memristor degradation. By measuring the current-voltage characteristics, the electrical conductivity of the memristor in low- and high-resistance operating modes was assessed. To determine the activation energy, the Arrhenius law and the provisions of the thermodynamics of irreversible processes were used, in particular the second postulate of Onsager, according to which the growth rate of the irreversible part of the entropy of a system tending to equilibrium is proportional to the sum of the products of the flows occurring in the system and the generalized thermodynamic force corresponding to each flow. The equilibrium state of the memristor was taken to be the state in which the memristor lost the ability to function as a resistive memory cell. The flow of Ag+ ions – electromigration was used as a substance flow. For the first process, the activation energy was 0.24 eV, and for the second, 1.16 eV. The different values of activation energy reflect the difference between the agglomeration mechanism of formation of a current-conducting channel, typical of an Ag/SnSe/Ge2Se3/W memristor, and the “standard” mechanism of substance transfer based on a group of point defects, which accompanies the process of memristor degradation.В мемристоре ионного типа Ag/SnSe/Ge2Se3/W определена энергия активации двух основных процессов, ответственных за его работу, а именно: энергия активации образования токопроводяшего канала и энергия активации деградации мемристора. С помощью измерения вольт-амперных характеристик оценена электропроводность мемристора в низко- и высокоомном режимах работы. Для определения энергии активации использованы закон Аррениуса и положения термодинамики необратимых процессов, в частности второй постулат Онзагера, согласно которому скорость роста необратимой части энтропии стремящейся к равновесию системы пропорциональна сумме произведений протекающих в системе потоков на соответствующую каждому потоку обобщенную термодинамическую силу. За равновесное состояние мемристора принимали состояние, в котором мемристор терял способность функционировать как ячейка резистивной памяти. В качестве потока вещества использовали поток ионов Ag+ — электромиграцию. Для первого процесса энергия активации составляла 0,24 эВ, а для второго — 1,16 эВ. Разные значения энергии активации отражают различие между агломерационным механизмом формирования токопроводящего канала, типичным для мемристора Ag/SnSe/Ge2Se3/W, и «стандартным» механизмом переноса вещества на основе группы точечных дефектов, сопровождающим процесс деградации мемристора

Моделирование вольт-амперной характеристики мемристора TiN/HfO2/Pt при различной толщине токопроводящего канала

The operation of the TiN/HfO2/Pt bipolar memristor has been simulated by the finite elements method using the Maxwell steady state equations as a mathematical basis. The simulation provided knowledge of the effect of conductive filament thickness on the shape of the I-V curve. The conductive filament has been considered as the highly conductive Hf ion enriched HfOx phase (x &lt; 2) whose structure is similar to a Magneli phase. In this work a mechanism has been developed describing the formation, growth and dissolution of the HfOx phase in bipolar mode of memristor operation which provides for oxygen vacancy flux control. The conductive filament has a cylindrical shape with the radius varying within 5–10 nm. An increase in the thickness of the conductive filament leads to an increase in the area of the hysteresis loop of the I-V curve due to an increase in the energy output during memristor operation. A model has been developed which allows quantitative calculations and hence can be used for the design of bipolar memristors and assessment of memristor heat loss during operation.Методом конечных элементов и с использованием в качестве математического базиса уравнений Максвелла в стационарном состоянии проведено моделирование работы биполярного мемристора TiN/HfO2/Pt, что позволило изучить влияние толщины токопроводящего канала на форму вольт-амперной характеристики. За токопроводящий канал принималась обогащенная ионами Hf фаза HfOx (x &lt; 2), имеющая структуру фазы Магнели, и, соответственно, обладающая повышенной электропроводностью. Разработан механизм образования, роста и растворения фазы HfOx в условиях биполярного режима работы мемристора, который позволяет управлять потоками кислородных вакансий. Токопроводящий канал имел форму цилиндра с радиусом, варьируемым в пределах 5—10 нм. Показано, что с увеличением толщины канала увеличивается и площадь гистерезисных петель вольт-амперной характеристики, что связано с возрастающей энергетической нагрузкой при работе мемристора. Разработана модель, которая позволяет проводить количественные расчеты и, следовательно,  может быть использована при конструировании биполярных мемристоров для оценки тепловых потерь во время их работы.

Investigation of the effect of preliminary modification of solutions on the properties of precipitated hydrated zirconium oxides

In this study, hydrated zirconium oxides and yttrium stabilized zirconia powders were synthesized by precipitation. Influence of preliminary solution modification, namely preliminary heating of the solutions and the addition of sulfate ions was investigated. It is shown that the addition of sulfate ions leads to a decrease in the size of aggregates and an increase in the specific surface area of the particles. The greatest increase in the specific surface area was observed during precipitation of a preliminary heated solution with the addition of sulfate ions. © Published under licence by IOP Publishing Ltd.Ministry of Education and Science of the Russian Federation, Minobrnauka: 14.581.21.0028, RFMEFI58117X0028Research and DevelopmentThe work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0006.The study was financially supported by the Ministry of Education and Science of the Russian Federation within the framework of subsidizing agreement of October 23, 2017 (No. 14.581.21.0028, unique agreement identifier RFMEFI58117X0028) of the Federal Target Program “Research and development in priority directions of the progress of the scientific and technological complex of Russia for the years 2014–2020.” 5. References [1] Chandra N, Singh D K, Sharma M, Upadhyay R K, Amritphale S S and Sanghi S K 2010 Journal of Colloid and Interface Science 342 327–332 [2] Si-Jia Hao, Cheng Wang, Tong-Le Liu, Zhi-Ming Mao, Zong-Qiang Mao, Jian-Long Wang 201