摘要
<p>We present studies of the thermal, magnetic, and electrical transport properties of polycrystalline PrBa<sub>2</sub>Cu<sub>4</sub>O<sub>8</sub> prepared at ambient oxygen pressure. Measurements of the low-temperature specific heat C(T) and magnetic susceptibility x(T) show similar results as in PrBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub>. An anomaly observed at 17 K in C(T) and dx/dT may be due to the antiferromagnetic ordering of the Pr sublattice. The upper limit of the entropy associated with the magnetic ordering is estimated to be 6.6 J/mol K. The free magnetic moment from a simple Curie-Weiss fit is 3.11<span style="font-size:12pt"><span style="font-family:Calibri,sans-serif"><span style="color:black"><span style="font-family:"新細明體","serif"">μ</span></span></span></span>B. These similarities in magnetic properties of PrBa<sub>2</sub>Cu<sub>3</sub>O<sub>7 </sub>and PrBa<sub>2</sub>Cu<sub>4</sub>O<sub>8</sub> suggest that the magnetic coupling mechanism might be mainly associated with the CuO<sub>2</sub> planes. The resistivity <span style="font-size:12pt"><span style="font-family:Calibri,sans-serif"><span style="color:black"><span style="font-family:"新細明體","serif"">ρ</span></span></span></span>(T) is nearly metallic from 1.5 to 300 K. Comparisons of samples prepared by different methods suggest that the anomaly in resistivity around 200 K may be extrinsic. The behavior of <span style="font-size:12pt"><span style="font-family:Calibri,sans-serif"><span style="color:black"><span style="font-family:"新細明體","serif"">ρ</span></span></span></span>(T) is rather puzzling and cannot be explained simply by a dimensional crossover of charge transport arising from the double CuO chains. Other similarities and differences of the mentioned physical properties between PrBa<sub>2</sub>Cu<sub>4</sub>O<sub>8</sub> and PrBa<sub>2</sub>Cu<sub>3</sub>O<sub>7 </sub>are stressed as well.</p>