Colossal thermoelectric power in charge ordered lanthanum calcium manganites (La0.5Ca0.5MnO3)

Abstract

Lanthanum calcium manganites (La 0.5 Ca 0.5 MnO 3) with a composition close to charge ordering, synthesized by high energy ball milling, was found to exhibit colossal thermoelectric power. Thermoelectric power (TEP) data was systematically analyzed by dividing the entire temperature range (5 K-300 K) into three different regimes to explore different scattering mechanisms involved. Mandal's model has been applied to explain TEP data in the region below the Curie temperature (T C). It has been found that the variation of thermoelectric power with temperature is pronounced when the system enters the charge ordered region at T < 200 K. For temperatures lower than 120 K, due to the coexistence of charge ordered state with a spin-glass state, the variation of thermoelectric power is maximum and exhibited a peak value of À80 mV/K at 58 K. This has been explained by incorporating Kondo properties of the spin-glass along with magnon scattering. FC-ZFC magnetization measurements indicate the existence of a glassy state in the region corresponding to a maximum value of thermoelectric power. Phonon drag contribution instead of spin-glass contribution is taken into account to explain TEP in the region 120 K < T < T C. Mott's polaronic contribution of charge carriers are considered to interpret TEP in the high temperature region (T > T C). The optimal Mn 4þ-Mn 3þ concentration in charge ordered La 0.5 Ca 0.5 MnO 3 was examined by X-ray Photoelectron Spectroscopy analysis which confirms the charge ordered nature of this compound. V

Connection of Thermopower, Magneto Thermopower with Resistivity and Magnetoresistivity in Nd&lt;sub&gt;(1-x)&lt;/sub&gt;Sr&lt;sub&gt;x&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; and Sm&lt;sub&gt;(1-x)&lt;/sub&gt;Sr&lt;sub&gt;x&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Manganites

“…Similar results were reported in earlier paper [1]. Increased value of S which reached hundreds of mV, was observed in some manganites near Curie temperature Т С [2][3][4]. Authors of this works linked it to the formation of polarons with small radiuses (small polarons) near Т С .…”

“…Authors of this works linked it to the formation of polarons with small radiuses (small polarons) near Т С . It is known that the small polarons are observed in non-magnetic semiconductors, and their occurrence only near Curie temperature in magnetic semiconductors is not discussed in [2][3][4]. Moreover, sizes of studied samples are not provided in works mentioned above, so no investigations concerning dependence of thermopower on volume were carried out.…”

Many-body renormalization of forces in f -electron materials

“…Many strongly-correlated materials exhibit properties useful for technological applications [4][5][6]. For example, the copper oxides and iron pnictides are high temperature superconductors [7][8][9], and the cobaltates exhibit colossal thermoelectric power [10] which is useful for energy conversion. Several vanadates have peculiar room-temperature metal-insulator transitions, allowing realization of a so-called "intelligent window," which becomes insulating as the external temperature drops [11][12][13][14].…”

Cвязь гигантских термоэдс, магнетотермоэдс, магнетосопротивления и намагниченности с магнитнопримесными состояниями в Nd-=SUB=-(1-x)-=/SUB=-Sr-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=- и Sm-=SUB=-(1-x)-=/SUB=-Sr-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=- манганитах

“…Повышенная величина S, достигавшая сотен милли-вольт, наблюдалась в некоторых манганитах в районе температуры Кюри T C [2][3][4], авторы которых объяс-няли ее образованием поляронов малого радиуса в районе T C . Известно, что поляроны малого радиуса наблюдаются в немагнитных полупроводниках, и их по-явление только в районе температуры Кюри магнитно-полупроводниковых манганитов авторы работ [2][3][4] ни-как не объясняли.…”

“…Известно, что поляроны малого радиуса наблюдаются в немагнитных полупроводниках, и их по-явление только в районе температуры Кюри магнитно-полупроводниковых манганитов авторы работ [2][3][4] ни-как не объясняли. Кроме того, в указанных статьях не приводятся размеры образцов и авторы, по-видимому, не изучали зависимость термоэдс от объема образца.…”