正方鎢青銅礦結構(Tetragonal Tungsten Bronze, TTB)的铌酸盐通常具有鐵電性，且此結構存在有三種不同的间隙位置可供攙雜。本研究之目的是將磁性離子加入TTB結構的铌酸盐中，使其同時具有鐵電性及鐵磁性，藉此發掘新穎的複鐵式材料。
TTB結構的铌酸盐成份較為複雜，固相燒結所得樣品中常含有雜相，給量測帶來不確定性，故本研究以液相自發成核的方式成長單晶樣品。已成功成長的單晶有Ba4La2Fe2Nb8O30、Ba6CoNb9O30、Ba6MnNb9O30、K2Nb4O11、Ba6Fe0.90Nb9.10O30及K4Fe1.56Nb6.44O21.4等。由於時間有限，本研究僅對其中的兩種晶體，即Ba6Fe0.90Nb9.10O30和K4Fe1.56Nb6.44O21.4的結構以及磁電性質進行了研究。
單晶X-ray繞射結果顯示，Ba6Fe0.90Nb9.10O30 具有正方晶系，空間群為P4/mbm，Fe取代Nb而非進入間隙位置。磁性測量顯示其可能呈現亞鐵磁性，且相轉變溫度在10 K以下。從結構分析以及介電系數隨溫度的變化推測，其可能具有鐵電特性，且相變化溫度大約在室溫附近。
單晶X-ray繞射結果顯示，K4Fe1.56Nb6.44O21.4並不屬於TTB結構，其空間群為Pnma。磁性測量顯示其亦可能在10 K以下呈現亞鐵磁性。此單晶在室溫下可測得電滯曲線，但明顯含有漏電流。由電滯曲線得出的剩餘極化量為9.25μC/cm2，矯頑電場為10.73kV/cm。

Tetragonal-tungsten-bronze (TTB) structured niobates usually exhibit ferroelectric properties. In the TTB crystal structure, there are three types of interstitial vacancies that may be used for doping various ions. The aim of this study is to discover novel multiferroic materials by filling the interstitial vacancies of the TTB structured niobates with various magnetic ions.
Owing to the complex composition of the TTB compounds, the samples prepared by the solid state sintering usually contain some secondary phases, causing confusing in the characterization. Therefore, attempts were made to grow single crystals from high temperature solution by the spontaneous nucleation method. The obtained single crystals are listed as follows: Ba4La2Fe2Nb8O30, Ba6CoNb9O30, Ba6MnNb9O30, K2Nb4O11, Ba6Fe0.90Nb9.10O30 and K4Fe1.56Nb6.44O21.4. However, due to the limited time available, only two of the crystals, i.e. Ba6Fe0.90Nb9.10O30 and K4Fe1.56Nb6.44O21.4 were selected for the structural, magnetic and electrical characterizations.
Single crystal X-ray diffraction (SC-XRD) showed that Ba6Fe0.90Nb9.10O30 had indeed the TTB structure with the space group P4/mbm and that Fe substituted with Nb, instead of entering the interstitial vacancies. Magnetic measurements showed that the crystal was potentially ferrimagnetic with the transition temperature below 10 K. Structural analysis and the measurements of dielectric constant versus temperature indicated that the crystal was likely to be ferroelectric and the transition temperature was around room temperature.
SC-XRD showed that K4Fe1.56Nb6.44O21.4 did not belong to the TTB structure. Its space group was Pnma. This crystal was possibly ferrimagnetic as well below 10 K. Ferroelectric hysteresis loops were registered at room temperature for this crystal, although they contained a large contribution of the leakage currents. The remanent polarization measured from the hysteresis was 9.25 μC/cm2 and the coercive field 10.73 kV/cm.

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