鈣鈦礦（ABO₃）結晶結構可視為由彼此共頂點的BO₆八面體構成之三維結構，A離子則位在BO₆八面體間形成的8至12配位空隙中。容差因子（Goldschmidt tolerance factor，t）利用結構中A、B、O離子半徑進行計算所得。當結晶結構為理想的鈣鈦礦（立方晶系）結構，容差因子將接近1。隨BO₆八面體於空間中的扭曲程度增加，結晶結構逐漸傾向四方、斜方對稱性時，計算所得之容差因子逐漸偏離1。故透過容差因子，可以評估鈣鈦礦結構中八面體於空間中扭曲程度與晶格結構對稱性。在鹼土金屬錫酸鹽鈣鈦礦序列中，隨著A位離子半徑由Ba²⁺（1.61 Å）、Sr²⁺（1.44 Å）遞減至Ca²⁺（1.34 Å），容差因子依序從1.02降至0.93。BaSnO₃維持立方結構，而SrSnO₃與CaSnO₃因八面體扭曲，屬GdFeO₃型斜方對稱。
本研究透過固態反應法合成CaSnO₃、SrSnO₃及BaSnO₃單晶與粉末樣品，並利用高解析X光粉末繞射(HR-XRD)與時間域熱反射(TDTR)技術，首次於一致實驗條件下系統性探討A位離子尺寸對錫酸鹽鈣鈦礦結構與熱性質之影響，建立了完整的晶格膨脹與單晶塊材熱導率數據。研究結果顯示，使晶體結構由高對稱性的立方相逐步轉變至低對稱性的斜方相，SnO₆八面體扭曲程度隨之增加。實驗中SrSnO₃在高溫下經歷兩階段相變(873K斜方Pbnm→Imma、1033K Imma→四方I4/mcm)，展現出複雜的晶格演化特性；而CaSnO₃則仍維持斜方晶系結構。而三材料在測試溫度範圍內皆表現出相近的體積熱膨脹行為，此現象主要來自於八面體扭曲程度變化、進而增加A-O12多面體空間之貢獻。熱傳導率量測結果則表明，隨著結構對稱性降低，晶體的熱傳導率降低且晶軸方向性差異減小，其中BaSnO₃具有最高的熱傳導率與顯著的異向性，而SrSnO₃與CaSnO₃的熱傳導效率明顯下降且方向性趨近。本研究之系統性結果對鈣鈦礦結構在結晶化學角度針對A位陽離子與物理性質之影響提供重要資訊，並有助於作為地球鈣鈦礦結構礦物結構轉變之物理性質趨勢演變之參考依據。

Perovskite stannates (ASnO₃, A = Ca, Sr, Ba) are useful for studying how crystal structure affects thermal properties. The stability of these materials depends on the size of the A-site ion, which controls octahedral distortion and lattice symmetry. This study synthesized CaSnO₃, SrSnO₃, and BaSnO₃ single crystals and powders using solid-state reactions and examined their thermal behaviors under the same experimental conditions.
High-resolution synchrotron powder X-ray diffraction showed that BaSnO₃ keeps its cubic symmetry, while SrSnO₃ and CaSnO₃ form orthorhombic phases with different SnO₆ octahedral distortions. Temperature-dependent diffraction revealed that SrSnO₃ goes through two phase transitions （Pbnm → Imma at 873 K, Imma → I4/mcm at 1033 K）, but CaSnO₃ stays orthorhombic phase from 298 to 1173 K. Even with different symmetries, all three compounds show similar volume thermal expansion coefficients, which reflects contributions from both octahedral tilting and A-O polyhedral changes.
We measured thermal conductivity using time-domain thermoreflectance （TDTR） on oriented single crystals. The results show that lower symmetry leads to lower conductivity and less anisotropy: BaSnO₃ has the highest conductivity and strong directional dependence, while SrSnO₃ and CaSnO₃ show reduced values and nearly isotropic transport. These results are new findings that link A-site cation size, lattice distortion, and phonon transport, providing insights into both functional oxide and understanding Earth perovskite materials.

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