Dielectric characterization of the BiFe0.5Cr0.5O3 ceramics

Dielectric properties of the BiFe0.5Cr0.5O3 ceramics synthesized under high pressure were investigated in a broad frequency range (20 Hz – 1 GHz) between 200 and 500 K. It was revealed that the ceramics exhibit electrical conductivity above 300 K. Below 300 K, a dielectric dispersion caused by ferroelectric domains was observed. It was found that the conductivity follows the Almond–West law, which allowed us to determine a DC contribution (σDC). From the σDC values obtained at different temperatures, the activation energy (EA = 0.302 ± 0.006 eV) was calculated using the Arrhenius law.publishe

Composition-, temperature- and pressure-induced transitions between high-pressure stabilized perovskite phases of the (1-x)BiFe0.5Sc0.5O3 - xLaFe0.5Sc0.5O3 series

Crystal structures of the high-pressure synthesized perovskite phases of the (1-x)BiFe0.5Sc0.5O3-xLaFe0.5Sc0.5O3 (0 ​= ​x ​≤ ​1) system and their temperature and pressure behaviours were studied using laboratory and synchrotron X-ray diffractions as well as neutron diffraction. At room temperature, the as-prepared phases with x ​≤ ​0.05 have an antipolar structure with the Pnma symmetry and with the √2ap ​× ​4ap ​× ​2√2ap superstructure (where ap is the pseudocubic perovskite unit-cell parameter). An incommensurately modulated phase with the Imma(00γ)s00 superspace group is observed for 0.10 ​= ​x ​≤ ​0.33, while a non-polar Pnma phase (√2ap ​× ​2ap ​× ​√2ap) is stable when x ​≥ ​0.34. The antipolar Pnma phase in the as-prepared samples with composition corresponding to x ​= ​0 transforms into the polar Ima2 one via irreversible annealing-caused transformation accompanied by a formation of a high-temperature intermediate polar R3c polymorph, while the antipolar Pnma phase in samples with x ​= ​0.05 is stable until the decomposition temperature. In the solid solutions with 0.10 ​= ​x ​≤ ​0.33, increasing temperature was found to result in a reversible transformation of the Imma(00γ)s00 phase into a non-polar Pnma one. The transition temperature decreases with increasing x. A hydrostatic pressure of few GPa was also shown to induce a reversible Imma(00γ)s00 → Pnma transformation.publishe

Sol-gel derived lanthanide-substituted layered double hydroxides Mg3/Al1-xLnx

Mg/Al/Ln (Ln = Nd, Sm, Eu) layered double hydroxides (LDHs) were synthesized using sol–gel method for the first time to the best our knowledge. The obtained materials were characterized by X-ray di raction analysis and fluorescence spectroscopy. The phase composition and luminescent properties of these LDHs were investigated and discussed. The Ln3+ substitution e ects were investigated in the Mg3Al1−xLnx LDHs by changing the Ln3+ concentration in the metal cation layers up to 10 mol%. It was demonstrated that only Mg3Al1−xEux LDHs showed luminescence properties, however, no any light emission was observed for the Mg3Al1−xNdx and Mg3Al1−xSmx LDH samplespublishe

Magnetic ordering in Co2+-containing layered double hydroxides via the low-temperature heat capacity and magnetisation study

The low-temperature heat capacity and the magnetisation of Co2+ n Al3+ layered double hydroxides (LDH) with the cobalt-to-aluminium ratio n = 2 and 3 and intercalated with different anions have been studied in a wide range of magnetic fields up to 50 kOe. The heat capacity, C(T), was found to demonstrate a Schottky-like anomaly observed as a broad local maximum in the temperature dependence below 10 K. The effect is caused by a splitting of the ground-state Kramers doublet of Co2+ in the internal exchange field and correlates with magnetic ordering in these LDH. In low applied fields, the temperature-dependent dc magnetic susceptibility demonstrates a pronounced rise, which is associated with an onset of magnetic ordering. Both the heat capacity anomaly and the magnetic susceptibility peak are more pronounced for the LDH with n = 2 than for those with n = 3. This feature is associated with an excess of the honeycomb-like Co–Al coordination (which corresponds to a 2:1 Co–Al ordering) over the statistical cation distribution in Co2Al LDH, while a rather random cobalt-aluminium distribution is typical for Co3Al LDH. The temperature of the Schottky-like anomaly measured in a zero field is independent of the interlayer distance. Application of the magnetic field results in a widening of the anomaly range and a shift to higher temperatures. The observed experimental data are typical for a cluster spin glass ground state.publishe

A comparative study of co-precipitation and sol-gel synthetic approaches to fabricate cerium-substituted Mg Al layered double hydroxides with luminescence properties

Mg/Al/Ce layered double hydroxides (LDHs) intercalated with carbonate and hydroxide anions were synthesized using co-precipitation and sol-gel method. The obtained materials were characterized by thermogravimetric (TG) analysis, X-ray diffraction (XRD) analysis, fluorescence spectroscopy (FLS) and scanning electron microscopy (SEM). The chemical composition, microstructure and luminescent properties of these LDHs were investigated and discussed. The Ce3 + substitution effects were investigated in the Mg3Al1 − xCex LDHs by changing the Ce3 + concentration in the metal cation layers from 0.05 to 10 mol%. It was demonstrated, that luminescence properties of cerium-substituted LDHs depend on the morphological features of the host lattice.publishe

Magnetic properties of the Bi0.65La0.35Fe0.5Sc0.5O3 perovskite

Magnetic properties of polycrystalline multiferroic Bi0.65La0.35Fe0.5Sc0.5O3 synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions were studied using a SQUID magnetometer technique. The temperature dependent static magnetic moment M was measured in both zero-field-cooled and field-cooled modes over the temperature range of 5-300 K in low magnetic field H = 0.02 kOe. The field dependent magnetization M(H) was measured in magnetic fields up to 50 kOe at different temperatures up to 230 K after zero-field cooling procedure. A long-range magnetic ordering of the antiferromagnetic type with a weak ferromagnetic contribution takes place below TN ≈ 220 K. Magnetic hysteresis loops taken below TN show a huge coercive field up to Hc ≈ 10 kOe, while the magnetic moment does not saturate up to 50 kOe. A strong effect of magnetic field on the magnetic properties of the compound has been found. Below TN ≈ 220 K the derivatives of the initial magnetization curves demonstrate the existence of a temperature-dependent anomaly in fields of H = 15÷25 kOe. The nature of the anomaly is unknown and requires additional study.publishe

Явление обменного сдвига в перовскитах (Nd₁₋хYx)₂/₃Ca₁/₃MnO₃ (x = 0; 0,1)

Обнаружен обменный сдвиг петель гистерезиса в соединениях (Nd₁₋хYx)₂/₃Ca₁/₃MnO₃ (x = 0; 0,1), возникающий при охлаждении в магнитном поле ниже температур магнитного упорядочения и свидетельствующий о магнитном фазовом расслоении этих соединений при низких температурах. Оценен вклад ферромагнитной фазы в полную намагниченность соединений. Обнаружено, что замещение неодима иттрием приводит к увеличению содержания ферромагнитной фазы в допированном соединении (Nd₀,₉Y₀,₁)₂/₃Ca₁/₃MnO₃ по сравнению с исходным соединением Nd₂/₃Ca₁/₃MnO₃. При этом ферромагнитная фаза в допированном соединении характеризуется меньшей коэрцитивной силой Hс и более прямоугольной петлей гистерезиса. Величина поля обменного сдвига HEB немонотонно зависит от магнитного поля охлаждения Нcool, и в области достаточно больших полей Нcool > 5 кЭ примерно вдвое меньше для допированного соединения. Такое различие определяется меньшей величиной обменного взаимодействия и большей величиной намагниченности насыщения ферромагнитной фазы в (Nd₀,₉Y₀,₁)₂/₃Ca₁/₃MnO₃.Виявлено обмінний зсув петель гістерезису у сполуках (Nd₁₋хYx)₂/₃Ca₁/₃MnO₃ (x = 0; 0,1), що виникає при охолодженні у магнітному полі нижче температур магнітного впорядкування та свідчить про магнітне фазове розшарування цих сполук при низьких температурах. Оцінено внесок феромагнітної фази в повну намагніченість сполук. Виявлено, що заміщення неодиму ітрієм призводить до збільшення змісту феромагнітної фази у допованій сполуці (Nd₀,₉Y₀,₁)₂/₃Ca₁/₃MnO₃ в порівнянні з базовою сполукою Nd₂/₃Ca₁/₃MnO₃. При цьому феромагнітна фаза в допованій сполуці характеризується меншою коерцитивною силою Hс та більш прямокутною петлею гістерезису. Величина поля обмінного зсуву HEB немонотонно залежить від магнітного поля охолодження Нcool, та в області досить великих полів Нcool > 5 кЕ приблизно вдвічі менше для допованої сполуки. Така різниця обумовлена меншою величиною обмінної взаємодії та більшою величиною намагніченості насичення феромагнітної фази в (Nd₀,₉Y₀,₁)₂/₃Ca₁/₃MnO₃.Exchange bias phenomenon evident of antiferromagnetic–ferromagnetic phase segregated state has been observed in (Nd₁₋хYx)₂/₃Ca₁/₃MnO₃ (x = 0; 0,1) compounds at low temperatures. A contribution to the total magnetization of the compounds due to the ferromagnetic phase has been evaluated. It has been found that yttrium doping leads to the growth of the ferromagnetic phase fraction. The ferromagnetic phase in the doped compound has a lower coercivity Hc and more rectangular form of the hysteresis loop. The values of the exchange bias field HEB and coercivity are found to be strongly dependent on the cooling magnetic field Нcool. In sufficiently high magnetic fields, Нcool > 5 kOe, the HEB value is approximately twice in the doped compound than in the parent compound. This difference is attributed to the lower exchange interaction and the higher saturation magnetization of the ferromagnetic phase in (Nd₀,₉Y₀,₁)₂/₃Ca₁/₃MnO₃