尖晶石材料MnV₂O₄結構與磁性關聯研究;Study on the Correlation of Structure and Magnetism in Spinel Material MnV₂O₄

Please use this identifier to cite or link to this item: https://ir.lib.ncu.edu.tw/handle/987654321/97829

Title:	尖晶石材料MnV₂O₄結構與磁性關聯研究;Study on the Correlation of Structure and Magnetism in Spinel Material MnV₂O₄
Authors:	魏無忌;Wei, Wu-Gee
Contributors:	物理學系
Keywords:	MnV₂O₄;尖晶石;過渡金屬氧化物;MnV₂O₄;spinel;transition metal oxides
Date:	2025-08-07
Issue Date:	2025-10-17 11:57:57 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文旨在探討以固態反應法合成之尖晶石結構材料Mn₁.₀₉V₁.₈₆O₄的基礎物理性質，透過一系列材料分析技術，包括X光粉末繞射（XPD）、中子粉末繞射(NPD)、穿透式電子顯微鏡（TEM）、拉曼光譜、介電性量測、鐵電性測試，以及物理量測（PPMS）分析，研究MnV₂O₄的結構與物理性質。結果顯示MnV₂O₄ 樣品為粒徑約 0.3–0.4 μm之多晶微米級顆粒。X光粉末繞和中子粉末繞射(NPD)的量測結果顯示樣，Mn、V和O的比例和結構為，Mn₀.₉₉OV₁.₈₆Mn₀.₁O₃(Mn₁.₀₉V₁.₈₆O₄)。選區電子繞射和高解析度TEM，顯示樣品為純相。Raman量測結果指出自80 K至300 K的溫度範圍內，皆維持穩定的立方晶系Fd3 ̅m空間群結構，未觀察到結構相變現象。搭配能量色散光譜（EDS）分析與 XRD結果，確認樣品具有組成均勻、純度高且結晶良好的單相特性。X光吸收光譜（XAS）進一步揭示，Mn元素之氧化態約等於 +2 價，V元素則約等於 +3 價。變溫中子繞射實驗顯示，Mn₁.₀₉V₁.₈₆O₄ 材料於約 52.5K 發生結構相變，並伴隨明顯的磁性轉變。低於此溫度，材料進入亞鐵磁性相，其磁性主要由 A site 原子貢獻，磁矩飽和值約為 4.38 μB/atom；相較之下，B site 原子的磁矩較小，約為 0.73 μB/atom，並與 A site 自旋方向呈現反平行排列。磁化率量測亦顯示材料在 53 K 發生磁相變，與中子繞射結果相符。進一步的磁滯曲線分析顯示，在 4 K 時具有明顯的磁滯現象，且飽和磁矩為 2.7 μB /f.u.，與中子繞射所推算出的理論值 0.9 μB/f.u.數量級相當。變溫拉曼光譜測量中，在650 cm⁻¹處觀察到對應 A1g與T2g之振動峰，約380 cm⁻¹處則對應Eg 模。此三種特徵峰於 80–300 K 間其頻率與相對強度均未呈現明顯變化，進一步驗證晶體結構在該溫區內穩定，亦未見熱脹冷縮或相變行為。在介電性分析方面，於升溫至 125 K 時，在低頻區（< 1 kHz）出現電容轉折行為，推測與缺陷極化（defect-related polarization）有關；然而，高頻區（> 0.01 MHz）並未顯示明顯差異，推論離子極化對溫度變化不具敏感性，此一結果亦與拉曼光譜的觀察一致。 ;This study aims to investigate the fundamental physical properties of the spinel-structured compound Mn₁.₀₉V₁.₈₆O₄ synthesized via the solid-state reaction method. A series of characterization techniques, including X-ray powder diffraction (XPD), neutron powder diffraction (NPD), transmission electron microscopy (TEM), Raman spectroscopy, dielectric measurements, ferroelectric testing, and physical property measurement system (PPMS) analysis, were employed to examine the structure and physical properties of MnV₂O₄. The results show that the MnV₂O₄ sample consists of polycrystalline particles with sizes ranging from approximately 0.3 to 0.4 μm. XPD and NPD measurements indicate that the chemical composition and structure correspond to Mn₀.₉₉OV₁.₈₆Mn₀.₁O₃, equivalent to Mn₁.₀₉V₁.₈₆O₄. Selected area electron diffraction (SAED) and high-resolution TEM analyses reveal that the sample is pure phase without any impurity. Raman spectra collected from 80 K to 300 K confirm a stable cubic phase with space group Fd-3̅m, with no signs of structural phase transitions within this temperature range. Combined with energy-dispersive X-ray spectroscopy (EDS) and XRD results, the sample is verified to be a high-purity, single-phase material with uniform composition and good crystallinity. X-ray absorption spectroscopy (XAS) further reveals that Mn and V ions are primarily in the +2 and +3 oxidation states, respectively. Temperature-dependent neutron diffraction measurements indicate a structural phase transition at approximately 52.5 K, accompanied by a significant magnetic transition. Below this temperature, the material enters a ferrimagnetic phase, with the magnetic moment mainly contributed by A-site atoms, reaching a saturation value of approximately 4.38 μB per atom. In contrast, B-site atoms exhibit smaller moments (~0.73 μB per atom) aligned antiparallel to the A-site spins. Magnetic susceptibility measurements also reveal a magnetic transition around 53 K, consistent with the neutron diffraction results. Further magnetic hysteresis analysis at 4 K shows a clear hysteresis loop with a saturation magnetization of 2.7 μB per formula unit, which is of the same order of magnitude as the theoretical value of 0.9 μB/f.u. derived from neutron data. In temperature-dependent Raman spectra, vibration modes corresponding to A1g and T2g appear around 650 cm⁻¹, while a peak near 380 cm⁻¹ corresponds to the Eg mode. The frequency and relative intensity of these three characteristic peaks remain largely unchanged across the 80–300 K range, further confirming the structural stability of the crystal without evidence of thermal expansion/contraction or phase transitions. In the dielectric analysis, a capacitance anomaly is observed around 125 K in the low-frequency region (< 1 kHz), which is presumed to be related to defect-induced polarization. However, no significant changes are found in the high-frequency region (> 0.01 MHz), suggesting that ionic polarization is not sensitive to temperature variations. This observation is consistent with the findings from Raman spectroscopy.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

Files in This Item:

File	Description	Size	Format
index.html		0Kb	HTML	24	View/Open

社群 sharing

Loading...