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首页> 外文期刊>Crystal growth & design >The Reversible alpha->beta Phase Transition of Cu_2AS_2O_7
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The Reversible alpha->beta Phase Transition of Cu_2AS_2O_7

机译：Cu_2AS_2O_7的可逆α->β相变

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摘要

Single crystals of copper(II)pyroarsenate(V),CU_2AS_2O_7,were prepared by chemical transport reactions in sealed and evacuated silica ampules starting from stoichiometric mixtures of the component oxides and chlorine as transport agent(temperature gradient 880-800 deg C,5 days).CU_2AS_2O_7 is dimorphous and shows a reversible a(low-temperature)<->beta(high-temperature)phase transition at 356(2)deg C detected by differential scanning calorimetry(DSC)and high-temperature X-ray powder diffraction(XRPD)measurements.The crystal structure of alpha-CU_2AS_2O_7(C2/c,Z=A,a=7.237(3),b=8.2557(17),c=9.780(3)A,beta=111.03(2)deg,R[F~2 > 2sigma(F~2)]=0.028)was determined from single-crystal data at room temperature.It crystallizes isotypically with alpha-Cu_2P_2O_7 and beta-Cu_2V_2O_7.The thortveitite-type crystal structure ofbeta-Cu_2As_2O_7(C2/m,Z=2,a=7.0987(3),b=8.2777(4),c=4.8666(2)A,beta=110.206(4)deg,R(Bragg)=0.1056)was determined by means of high-temperature XRPD recorded at 400 deg C.The crystal structures of both polymorphs are closely related and consist of infinite sheets of [CuOJ polyhedra(a:x=5;beta:x=6)and interjacent AS_2O_7 anions that occur either in a bent(As-O-As)configuration((X-CU_2AS_2O_7,bridging angle 145.9(2)deg)or in a linear(As-O-As)configuration(beta-CU_2AS_2O_7).alpha-Cu_2As_2O7 was further characterized by vibrational spectroscopy.Its IR and Raman spectra are discussed on the basis of a factor group analysis.
机译：通过在密封和抽空的二氧化硅安瓿中通过化学传输反应，从成分氧化物和氯作为传输剂的化学计量混合物开始，制备焦亚砷酸铜（V）单晶CU_2AS_2O_7，其单晶（温度梯度为880-800℃，5天）.CU_2AS_2O_7是双晶的，并且通过差示扫描量热法（DSC）和高温X射线粉末衍射检测到在356（2）℃时显示可逆的a（低温）-β（高温）相变（XRPD）测量.α-CU_2AS_2O_7（C2 / c，Z = A，a = 7.237（3），b = 8.2557（17），c = 9.780（3）A，beta = 111.03（2）deg的晶体结构，R [F〜2> 2sigma（F〜2）] = 0.028）是在室温下从单晶数据确定的。它通过α-Cu_2P_2O_7和β-Cu_2V_2O_7同型结晶.β-Cu_2As_2O_7（S）的百变沸石型晶体结构C2 / m，Z = 2，a = 7.0987（3），b = 8.2777（4），c = 4.8666（2）A，beta = 110.206（4）deg，R（Bragg）= 0.1056）通过在400摄氏度下记录的高温XRPD。两种多晶型物的全部结构密切相关，并由无限张的[CuOJ多面体（a：x = 5;β：x = 6）和相邻的AS_2O_7阴离子以弯曲（As-O-As）构型（（ X-CU_2AS_2O_7，桥接角145.9（2）deg或呈线性（As-O-As）构型（β-CU_2AS_2O_7）.α-Cu_2As_2O7的振动光谱进一步表征，在此基础上讨论了其IR和拉曼光谱因子组分析。

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