The polycrystalline CuFeO₂ (CFO) and CuFe_1-xM_xO₂ (M = Ti, Hf, Zr, M-CFO) samples are synthesized by solid-state reaction method. The doping effect of tetravalent nonmagnetic transition metal M⁴⁺ ions on the microstructure, defect evolution, and magnetic and magnetocaloric properties of the CFO system are comparatively investigated. The substitution of M⁴⁺ for Fe³⁺ increases lattice parameters, changes the bond length of Fe/Cu-O and bond angle of Fe-O-Fe, and improves the microstructure to some extent. Positron annihilation spectroscopy results indicate that M⁴⁺ doping induces the agglomeration of small-sized vacancy defects manifested as the increase in vacancy-type defect size and the suppression of inherent defect concentration. Magnetic measurements show that the antiferromagnetic stability of CFO system is clearly affected by M⁴⁺ doping, and Ti⁴⁺ doping has a more noticeable impact than Hf⁴⁺ and Zr⁴⁺ doping. Meanwhile, the coexistence of weak ferromagnetism and antiferromagnetism is detected in all doped samples, while Ti-doped system exhibits extraordinary magnetic properties. Especially for Ti-CFO2 (x = 0.03) sample, the maximum magnetization reaches as high as 11.81 emu/g at 0.5 T, which enhanced one order of magnitude than that of undoped CFO. Isothermal M-H data at different temperatures show that entropy change (ΔS_M) and refrigerant capacity (R_C) for CFO and M-CFO2 samples are significantly weakening with M⁴⁺ substitution in bulk CFO. The maximum ΔS_M = 4.79 J·kg⁻¹ K⁻¹ and R_C = 12.79 J·kg⁻¹ for undoped CFO are obtained near the transition temperature T_N2 = 12 K, with the applied fields up to 6 T. The possible reasons for the above observations are discussed in detail.

中文翻译：

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过渡金属离子掺杂对CuFeO 2陶瓷的微观结构，缺陷演变以及磁热磁性能的影响

通过固相反应法合成了多晶CuFeO ₂（CFO）和CuFe _{1- x} M _x O ₂（M  = Ti，Hf，Zr，M -CFO）样品。比较研究了四价非磁性过渡金属M ⁴⁺离子对CFO系统的微观结构，缺陷演变以及磁热和磁热性能的掺杂作用。用M ⁴⁺代替Fe ^3+可以增加晶格参数，改变Fe / Cu-O的键长和Fe-O-Fe的键角，并在一定程度上改善显微组织。正电子an没光谱结果表明M ⁴⁺掺杂引起小尺寸空位缺陷的聚集，表现为空位型缺陷尺寸的增加和固有缺陷浓度的抑制。磁性测量表明，CFO系统的反铁磁稳定性明显受到M ⁴⁺掺杂的影响，并且Ti ⁴⁺掺杂的影响比Hf ⁴⁺和Zr ⁴⁺掺杂的影响更大。同时，在所有掺杂样品中都检测到弱铁磁性和反铁磁性的共存，而钛掺杂系统表现出非凡的磁性。特别是对于Ti-CFO2（x = 0.03）的样品，在0.5 T时最大磁化强度高达11.81 emu / g，这比未掺杂的CFO增强了一个数量级。等温中号- ħ在不同温度下的数据显示，熵变（Δ小号_中号）和制冷剂容量（ř _ç用于CFO和）中号-CFO2样品被显著削弱中号⁴⁺散装CFO置换。在转变温度T _N2附近获得未掺杂CFO的最大ΔS _M  = 4.79 J·kg ^-1  K ^-1和R _C  = 12.79 J·kg ^-1 = 12 K，施加的磁场最高达6T。将详细讨论上述观察的可能原因。