The thermal behaviour of a natural allanite-(Ce) has been investigated up to 1073 K (at room pressure) by means of in situ synchrotron powder X-ray diffraction and single-crystal neutron diffraction. Allanite preserves its crystallinity up to 1073 K. However, up to 700 K, the thermal behaviour along the three principal crystallographic axes, of the monoclinic β angle and of the unit-cell volume follow monotonically increasing trends, which are almost linear. At T > 700–800 K, a drastic change takes place: an inversion of the trend is observed along the a and b axes (more pronounced along b) and for the monoclinic β angle; in contrast, an anomalous increase of the expansion is observed along the c axis, which controls the positive trend experienced by the unit-cell volume at T > 700–800 K. Data collected back to room T, after the HT experiments, show unit-cell parameters significantly different with respect to those previously measured at 293 K: allanite responds with an ideal elastic behaviour up to 700 K, and at T > 700–800 K its behaviour deviates from the elasticity field. The thermo-elastic behaviour up to 700 K was modelled with a modified Holland–Powell EoS; for the unit-cell volume, we obtained the following parameters: V_T0 = 467.33(6) Å³ and α_T0(V) = 2.8(3) × 10^–5 K⁻¹. The thermal anisotropy, derived on the basis of the axial expansion along the three main crystallographic directions, is the following: α_T0(a):α_T0(b):α_T0(c) = 1.08:1:1.36. The T-induced mechanisms, at the atomic scale, are described on the basis of the neutron structure refinements at different temperatures. Evidence of dehydroxylation effect at T ≥ 848 K are reported. A comparison between the thermal behaviour of allanite, epidote and clinozoisite is carried out.

已通过原位同步加速器粉末 X 射线衍射和单晶中子衍射研究了天然阿兰石 (Ce) 在高达 1073 K（室温下）的热行为。Allanite 保持其结晶度高达 1073 K。然而，高达 700 K，沿三个主晶轴、单斜β角和晶胞体积的热行为遵循单调增加的趋势，几乎是线性的。在Ť  > 700-800 K，急剧变化发生：沿观察到的趋势的反转一个和b轴（沿更加明显b）和单斜晶系β角度；相反，沿着所述观察到的膨胀的异常增加Ç轴，其控制通过在单元电池容积经历的积极趋势Ť  > 700-800 K.收集的数据返回到室温Ť时，H后Ť实验中，显示晶胞参数与之前在 293 K 下测量的参数显着不同：allanite 以理想的弹性行为响应，最高可达 700 K，而在T  > 700–800 K 时，其行为偏离弹性场。高达 700 K 的热弹性行为是用改进的 Holland-Powell EoS 建模的；对于晶胞体积，我们获得了以下参数：V _T0  = 467.33(6) Å ³和 α_T0 ( V ) = 2.8(3) × 10 ^–5  K ^-1。基于沿三个主要结晶方向的轴向膨胀导出的热各向异性如下：α _T0 ( a ):α _T0 ( b ):α _T0 ( c ) = 1.08:1:1.36。原子尺度上的T诱导机制是根据不同温度下的中子结构细化来描述的。 报告了在T ≥ 848 K时脱羟基作用的证据。进行了褐铝石、绿帘石和斜纹石的热行为之间的比较。