Optical coherence lifetimes and decoherence processes in erbium-doped lithium niobate (Er$^{3+}$:LiNbO$_3$) crystalline powders are investigated for materials that underwent different mechanical and thermal treatments. Several complimentary methods are used to assess the coherence lifetimes for these highly scattering media. Direct intensity or heterodyne detection of two-pulse photon echo techniques was employed for samples with longer coherence lifetimes and larger signal strengths, while time-delayed optical free induction decays were found to work well for shorter coherence lifetimes and weaker signal strengths. Spectral hole burning techniques were also used to characterize samples with very rapid dephasing processes. The results on powders are compared to the properties of a bulk crystal, with observed differences explained by the random orientation of the particles in the powders combined with new decoherence mechanisms introduced by the powder fabrication. Modeling of the coherence decay shows that paramagnetic materials such as Er$^{3+}$:LiNbO$_3$ that have highly anisotropic interactions with an applied magnetic field can still exhibit long coherence lifetimes and relatively simple decay shapes even for a powder of randomly oriented particles. We find that coherence properties degrade rapidly from mechanical treatment when grinding powders from bulk samples, leading to the appearance of amorphous-like behavior and a broadening of up to three orders of magnitude for the homogeneous linewidth even when low-energy grinding methods are employed. Annealing at high temperatures can improve the properties in some samples, with homogeneous linewidths reduced to less than 10 kHz, approaching the bulk crystal linewidth of 3 kHz under the same experimental conditions.
Effects of fabrication methods on spin relaxation and crystallite quality in Tm-doped Y$_2$Al$_5$O$_{12}$ powders studied using spectral hole burning
高质量的稀土离子掺杂材料是量子存储器、超高分辨率光谱分析仪和信息处理等应用的先决条件。与散装材料相比，REI掺杂粉末提供低成本制造和更大范围的可访问材料系统。在这里，我们表明，晶体性能，如核自旋寿命，受到强烈的影响，机械处理，光谱烧孔可以作为一种敏感的方法来表征稀土掺杂粉末的质量。我们专注于掺铥的Y $_2$ Al $_5$ O $_{12}$（Tm：YAG）的具体情况。不同的方法获得的粉末进行了比较和退火的粉末光谱质量的影响进行了研究的几个例子。我们的结论是，退火可以扭转粉末制造的一些不利影响，在某些情况下，可以达到散装材料的性能。我们的结果可能适用于其他杂质和其他晶体，包括纳米结构金刚石中的色心。
Unusual effects of manual grinding and subsequent annealing process observed in Gd5.09Ge2.03Si1.88 compound
Gd5.09Ge2.03Si1.88化合物以及其他磁热材料肯定不会在未来的磁制冷应用或其他设备中以其未制造的铸态条件使用。本文研究了不同工艺制备Gd5.09Ge2.03Si1.88复合材料，主要包括铸态粉末、退火粉末和压制烧结粉末。退火粉末（1370 K / 20小时）不存在单斜相和在铸态粉末中观察到的一级磁结构转变。压制和烧结的粉末也不存在一级相变。此外，压实压力将二阶磁性转变转移到较低的温度。作为压实压力的函数的电池参数的行为表明，TC是由参数c的变化直接影响。
Micro-cracking, microstructure and mechanical properties of Hastelloy-X alloy printed by laser powder bed fusion: as-built, annealed and hot-isostatic pressed
Cobalt Substitution in CuFe$_{2}$O$_{4}$ spinel and its influence on the crystal structure and phonons
本文采用聚合物前驱体法，在700 ~ 1200 ${}^\circ$ C的不同退火温度下，制备了纳米尖晶石Co ${}_{1-x}$ Cu ${}_{x}$ Fe ${}_{2}$ O ${}_{4}$粉末。通过X射线粉末衍射对样品进行了表征，证实了CoFe ${}_{2}$ O ${}_{4}$样品为理想的反尖晶石结构，CuFe ${}_{2}$ O ${}_{4}$样品为四元畸变的反尖晶石结构。基于FWHM评估，我们估计未取代样品的微晶尺寸在27和37 nm之间变化。通过红外光谱和拉曼光谱确定了光学活性模式。混合样品的声子谱表现出局部四阶畸变。
Residual stress induced stabilization of martensite phase and its effect on the magneto-structural transition in Mn rich Ni-Mn-In/Ga magnetic shape memory alloys
