Thermal conductivity of crystals formed by fluoritelike phases in MF-RF3 systems (M = Li, Na, and K, R = Rare Earth)

The temperature dependence of the thermal conductivity for laser media based on fluoride crystals was determined and its relationship with the degree of ordering in the crystal structure of these materials was found. All crystals were grown by the method of vertical directional crystallization in graphite crucibles, while 20 to 41-mm-long cylindrical samples 4 10 mm in diameter were used for measurements. The results show that the maximum value of the thermal conductivity corresponds to the LiYF4:Nd3+ crystal containing only light elements. The combination in equivalent crystallographic positions of Y and Yb ions with a large difference in the ionic sizes and with an even larger difference in masses leads to pronounced phonon scattering and a lower thermal conductivity. The results obtained for NYF-type crystal correspond to the growth of thermal conductivity with temperature

Effect of the valence state of ce ions on the phase stability and mechanical properties of the crystals of ZrO<inf>2</inf>-based solid solutions

© 2017, Pleiades Publishing, Ltd. The structure and mechanical properties of the crystals of solid solutions of zirconium dioxide, which are stabilized by yttrium and cerium oxides, have been studied. The electron paramagnetic resonance technique has been used to identify Ce 3+ ions and to determine their relative concentration in the crystals. It is shown that the presence of Ce 3+ ions in the crystals is the main factor responsible for their high fracture toughness. The annealings carried out during investigations, which lead to a decrease in the concentration of Ce 3+ ions, show that a change in the valence state of cerium ions lowers the fracture toughness of the crystals

編集委員

© 2017, Pleiades Publishing, Ltd. The structure and mechanical properties of the crystals of solid solutions of zirconium dioxide, which are stabilized by yttrium and cerium oxides, have been studied. The electron paramagnetic resonance technique has been used to identify Ce 3+ ions and to determine their relative concentration in the crystals. It is shown that the presence of Ce 3+ ions in the crystals is the main factor responsible for their high fracture toughness. The annealings carried out during investigations, which lead to a decrease in the concentration of Ce 3+ ions, show that a change in the valence state of cerium ions lowers the fracture toughness of the crystals

ИЗУЧЕНИЕ КРИСТАЛЛОВ ЧАСТИЧНО СТАБИЛИЗИРОВАННОГО ZRO2 ЛЕГИРОВАННЫХ CE МЕТОДОМ ЭЛЕКТРОННОГО ПАРАМАГНИТНОГО РЕЗОНАНСА

The study of crystals of ZrO2 solid solutions (PSZ) stabilized with yttrium and cerium oxides was carried out by electron paramagnetic resonance (EPR) in the X and Q range. The presence of Zr3+ centers in annealed ZrO2 crystals stabilized only by yttrium oxide (2.8 mol.% Y2O3) is established. Another kind of paramagnetic O−centers appear when CeO2 is added to ZrO2 crystals in addition to yttrium oxide. To estimate the concentration of Ce3+ ions in PZS crystals, EPR spectra were recorded in the presence of a reference specimen at 7 K. Paramagnetic Ce3+ ions have been identified and their relative amounts in PSZ crystals before and after high−temperature heat treatment has been measured. The annealing in air leads to a decrease in the concentration of Ce3+ ions for all compositions and changes the color of the crystals from red to white. After annealing in the 2.0Y0.8Ce3Zr sample, the amount of paramagnetic Ce3+ ions decreased approximately twice. Paramagnetic centers from Ce3+ are not detected in a the sample with a low cerium content of 0.1 mol.% after annealing which indicates the complete transition of Ce3+ to the Ce4+ state. It is shown that the formed paramagnetic centers of cerium are bound by strong exchange interactions. No angular dependence of the EPR lines for the paramagnetic Ce3+ cations on the applied external magnetic field was observed. The probable reason for the absence of such angular dependence is that impurity rare−earth ions are located next to each other, forming impurity clusters with effective spin Seff = 1/2.Проведено исследование кристаллов твердых растворов ZrO2 (ЧСЦ), стабилизированных оксидами иттрия и церия, методом электронного парамагнитного резонанса (ЭПР) в X− и Q−диапазоне. В отожженных кристаллах ZrO2 стабилизированных только оксидом иттрия (2,8 % (мол.) Y2O3) установлено присутствие Zr3+ центров. При добавлении СeO2 к кристаллам ZrO2, помимо оксида иттрия, проявляется другой вид парамагнитных O–−центров. Для оценки концентрации ионов Ce3+ в кристаллах ЧСЦ зарегистрированы спектры ЭПР в присутствии эталона при температуре 7 К. Идентифицированы парамагнитные ионы Ce3+ и их относительное количество в кристаллах ЧСЦ до и после высокотемпературной термообработки. Показано, что проведенные в работе отжиги на воздухе, приводят к уменьшению концентрации ионов Ce3+ для всех составов, а также изменяют цвет кристаллов с красного на белый. В образце 2,0Y0,8CeZr после отжига количество парамагнитных ионов Ce3+ уменьшилось примерно в два раза. В образце с малым содержание церия (0,1 % (мол.)) после отжига парамагнитные центры от Ce3+ не регистрируются, что говорит о полном переходе Ce3+ в состояние Ce4+. Показано, что образованные парамагнитные центры церия, связаны сильными обменными взаимодействиями. Угловая зависимость ЭПР линий от парамагнитных катионов Ce3+ от приложенного внешнего магнитного поля не наблюдалась. Вероятной причиной отсутствия угловой зависимости является то, что примесные редкоземельные ионы расположены рядом друг с другом, образуя примесные кластеры с эффективным спином Seff = 1/2

Thermal conductivity of crystals formed by fluoritelike phases in MF-RF3 systems (M = Li, Na, and K, R = Rare Earth)

The temperature dependence of the thermal conductivity for laser media based on fluoride crystals was determined and its relationship with the degree of ordering in the crystal structure of these materials was found. All crystals were grown by the method of vertical directional crystallization in graphite crucibles, while 20 to 41-mm-long cylindrical samples 4 10 mm in diameter were used for measurements. The results show that the maximum value of the thermal conductivity corresponds to the LiYF4:Nd3+ crystal containing only light elements. The combination in equivalent crystallographic positions of Y and Yb ions with a large difference in the ionic sizes and with an even larger difference in masses leads to pronounced phonon scattering and a lower thermal conductivity. The results obtained for NYF-type crystal correspond to the growth of thermal conductivity with temperature

Thermal conductivity of crystals formed by fluoritelike phases in MF-RF3 systems (M = Li, Na, and K, R = Rare Earth)

The temperature dependence of the thermal conductivity for laser media based on fluoride crystals was determined and its relationship with the degree of ordering in the crystal structure of these materials was found. All crystals were grown by the method of vertical directional crystallization in graphite crucibles, while 20 to 41-mm-long cylindrical samples 4 10 mm in diameter were used for measurements. The results show that the maximum value of the thermal conductivity corresponds to the LiYF4:Nd3+ crystal containing only light elements. The combination in equivalent crystallographic positions of Y and Yb ions with a large difference in the ionic sizes and with an even larger difference in masses leads to pronounced phonon scattering and a lower thermal conductivity. The results obtained for NYF-type crystal correspond to the growth of thermal conductivity with temperature